Star Wars is 6 movies plus an expanded universe probably invisible to 95% of the population that saw those movies.
Star Trek has a much narrower audience and is more demanding on its fans. There is a lot of continuity you need to keep track of. You are looking at spending over a grand buying it all on DVD. 10 movies. 6 tv shows with over 800 episodes.
Considering the success and mainstream acceptance of franchises that are as or even more nerdy than Star Trek (Harry Potter, Lord of the Rings), I'm beginning to think that it's less about content and more about how "into" it people get.
Star Trek was (mostly) weekly television. Over the course of a year, a casual fan could be expected to watch around 20 hours of it. More, if there was more than one spin-off running at the same time, or if one of the many movies was released that year.
With Star Wars over that same year you could expect a casual fan to see either none of it, or two hours worth, depending on if there was a movie released that year. Yeah, Star Wars has a gigantic expanded universe, but the average joe is barely literate, proud of the fact that he hasn't read a book since high school, never set foot in a library or bookstore and completely unaware that the SWEU even exists. So that doesn't really hurt Star Wars the way oversaturation hurt Trek.
I think these are very siginificant points.
Generally speaking, nothing is less cool than being deeply into something and obsessing about it and being committed to it. That is the Way of the Nerd. Cool, on the other hand, tends to be about the appearance of effortlessness. It takes very little effort to get into Star Wars: watch half a dozen movies and you're done. You can do it in a day.
Star Trek? Ten movies and several hundred episodes. That's a major commitment.
Both properties have plenty of other things you can get into, books, games, comics, etc, but most fans of any TV or movie series ignore all that. Of course, if you say SW is cool and ST is lame or nerdy and then go on to debate old Clone Wars vs new Clone Wars or talk about the development of Mandalorian culture in Jeter's novels as opposed to Traviss's, everyone around you should and will laugh at you and call you a nerd.