Confession: I think the last time I delved into fan fiction, as a reader, was back in the nineties when I was writing a non-fiction book on XENA: WARRIOR PRINCESS and felt obliged to explore the fanfic -- for research purposes
Greg and Jim speak for me as well. I love fanfic, and have written a ton of fanfic -- including a Highlander/Hercules/Xena crossover fanfic that I wrote with my first wife back in the 1990s that I'm actually quite proud of, not to mention a bunch of Marvel fanfic I did with some friends on the GEnie bulletin board waybackwhen -- but I avoid reading it for practical and legal reasons and I avoid writing it for financial reasons, as Greg said.
I never really got into fanfic much, either reading or writing. There was just so much professional SF/fantasy to read. And I didn't really participate in fandom or have many friends who did, so I didn't have access to fanzines anyway. Once the Internet came along, I was sometimes curious about the fanfic I might find there, but I didn't know how to sort out the good stuff from the rest, so I was hesitant to give it a try. As for writing, I did write a couple of Trek fanfics in high school, but I think only one friend ever read them, and I always saw it as practice for a professional career (since I settled on writing as my career goal when I was 13). And I put most of my creative energy into building my own original universes. I've always loved worldbuilding, and if anything, it's always been easier for me to develop a universe than to come up with specific story ideas that take place in it.
It's funny. Periodically, I wistfully express a desire to write in some universe that I've never had the opportunity to do a tie-in for. At which point some well-meaning soul often suggests that I just go ahead and write, say, a CLEOPATRA 2525 novel for fun. Cue awkward explanation about how this isn't really financial feasible for us freelancers.
As a reader I never really got into fanfic despite having friends in that community. I just found the archives and forums of the time practically impenetrable, and didn't have a good way of identifying the stuff I would enjoy among all the stuff that wasn't my thing. It's been interesting over the years watching things like Lulu and Amazon and especially systems like Kindle Unlimited make the self-publishing model viable to anyone who wants their words out there. Looped back around to a whole world of stuff where it can be very difficult to find the signal in the noise.
This is where I show my age by recalling that I wrote my teenage fanfic by hand in spiral notebooks, long before the internet or word processors, and that I also remember when fanfic circulated via stapled, mimeographed, booklets sold and shared at conventions. Fanfic predates internet forums and archives by decades, even though nowadays I sometimes see it discussed (even by journalists) as though fanfic only ever existed on-line.
What @Greg Cox said times a billion. Typewriters were a godsend in the 1970s and 1980s when I was a kid and hated writing by hand but could touch type (I learned how to touch type in the seventh grade, and never looked back), but once computers became a thing, typewriters became about as useful as a telephone operator is today.
Oh, don't get me wrong, the backspace key is a godsend for my clumsy fingers. It's not about utility. It's more of a nostalgia for the machines themselves, the way they looked and felt and sounded, and the ingenuity of their design and function. Plus, to me as a child, typewriters were the things that writing happened on, the things that produced books and articles and newspaper stories, and that made them immensely cool. We had a big old Royal typewriter that I think was a hand-me-down from my grandfather, and that was a classy old thing, but I was proud when I got a typewriter of my own that I could keep in my room and write stuff on. I even had a compact portable one that I could cover with a lid and carry around like a small suitcase, so I could take it with me to school or on a trip. It didn't always work that well, but it was mine, and I did some of my earliest fiction writing on it, and sometimes I miss it. Besides, are the frustrations of a typewriter's keys jamming or the ribbon tangling or using Liquid Paper on typos any worse than the frustrations of a printer refusing to work right when you need it to, or a laptop crashing on you? At least with a typewriter, you could easily identify and fix its malfunctions. All its mechanisms were right there in front of you, nothing hidden. (Well, at least with a manual typewriter, as opposed to the electric ones. I only ever really used those in typing class at school.)
Oh, sure. It's always important to do research, to consult whatever sources you can find on the subject you're writing about. Of course, some of the published manuals are more conjectural than others or have details that have been superseded, but they can be a source of ideas.
Re: typewriters, I still remember carrying a 30-pound (typebar!) "portable" electric typewriter full-tilt up the hill at CSU Long Beach, to finish my late English History term paper in (or at least close to) the department office. And having a temporary visual impairment from running full-tilt uphill while carrying an extra 30 pounds. And when writing very short stuff for Museum projects, I've been known to compose my thoughts directly on a Linotype.
I remember reading Barbara Hambly's Crossroad and it being immediately clear she was describing the walking routes between different rooms from the old Franz Joseph Star Trek Blueprints. More recently, one of those Kelvinverse Starfleet Academy books borrowed their starship deck layouts from Lora Johnson's Mr. Scott's Guide to the Enterprise and having to cool myself off because the Kelvinverse ships are meant to be much much bigger (which I was furiously arguing here at the time)
I've got a big reference shelf of books within easy reach for when I'm writing Star Trek - the Encyclopedia and Star Charts get the most use, but I also have the various series companions, the Chronology, Starfleet Survival Guide and the Technical Manuals to hand. Even some of the older, less canonical stuff like the Starfleet Medical Reference Manual, Spaceflight Chronology, FASA roleplaying game supplements and various deck plans come in useful for inspiration.
I just read Hambly's Ghost Walker, and it does the same -- to the point I almost pulled my copy of the Franz Joseph blueprints off the shelf to trace routes.
Why do you write? How have your motivations changed (if at all) compared with before and during your career as a professional writer?
I don't feel I have a choice in the matter. One day when I was 13, I told myself a complete story in my head and realized I was already a writer. From that moment on, I knew that was what I'd do with my life. And I just can't be satisfied with a job that doesn't let me use my mind. The only other jobs I've had that I enjoyed at all (not that I've had many) were shelving jobs in bookstores and libraries, since I like the mental exercise of organizing things, and I like being around books. Only in the sense that I've had to give priority to making a living and not going broke, sometimes at the expense of a purely creative focus. Though that's more a change in emphasis than purpose, forced by circumstances.
You ask that as if I have a choice in the matter...! I'm drawn to write, I'm compelled to do it. It's something I've been doing ever since I knew that I could, and the fact that I got to make a career out of it is just a bonus. I think what motivates me remains the same. As soon as I realized that I could make a living as a writer, that was the path I wanted to take. I love writing, I'm passionate about it, and I've tried to center that in all the work that I do. I'm 25 years into this now, so sure, I've grown into being a professional writer, but the drive to write still comes from the same place - the impulse that says wouldn't it be cool to tell this story...