You only have to look at Star Trek Online to see the ridiculous amounts of money people will throw at you for the right starship.
I guess it comes down to investment; with TOR they have so many other things in development, and they have to do it all on a budget, it might be difficult to justify the expense when it seems not have not payed off quite as well as they'd hoped.
Personally, I think more people would play if there were were variety; GSF is a load of fun, but it can be a bit monotonous because there are so few maps and game modes to play.