More power to you. S&S used to periodically do collected stories written by fans. I recall there were a number of conditions and they had to be short stories basically. But IIRC a few of our resident novelists may have started that way--though I don't recall who. But it's been a while since they did that.
The Strange New Worlds anthologies were not "fan fiction collections" as they're often misrepresented to be. They were more along the lines of the L. Ron Hubbard Writers of the Future contest anthologies -- an opportunity for novice writers to get their first (or second or third) professional credits. Fan fiction means fiction written purely for recreation. SNW was about giving aspiring professional writers a chance to break into the field. It wasn't writing for fun, it was applying for a job.
Note that a few SNW writers have gone on to have substantial writing careers outside of Star Trek. For example, Geoffrey Thorne has gone on to become a TV writer-producer on shows such as Leverage and The Librarians, while R.S. Belcher and Robert T. Jeschonek have become known for their original fantasy novels. SNW wasn't just for people who liked Star Trek, it was for people who wanted to be professional writers.
It does sound like it's incredibly difficult to get to be an official tie-in writer these days. It sounds like you have to basically establish yourself before you can even be considered to be a novelists for Star Trek.
Being a pro writer takes a lot of commitment and years of hard work and perseverence in the face of constant rejection. It's not enough just to love Star Trek; you have to love writing in and of itself, to have a passion for creating whether it's in your favorite franchise or worlds of your own invention. A writing career means you frequently fail to sell the specific stories you want to tell, so that you have to change course and try something else and something else until one thing or another finally works. If your entire ambition is to do only one thing, then you're unlikely to get anywhere.
Heck, it's like any other career. There are only so many job openings at a given company, so you have to be willing to apply for jobs elsewhere if you want to get work.