X-men and Avengers both had successful spinoffs (and prequels), which Superman and Batman are trying to compete with by doing a Justice league movie (why Ben Affleck?). Plus, I'm sure if Avengers could get their hands on Spiderman, they would. People don't just want the norms.
But you're talking about things that run concurrently with their successful parents or where the parent is still there and new elements are added.
The simple fact of the matter is this: with each spinoff, people became less and less interested in Star Trek. So if I'm a studio/network executive, the question is this: if I greenlight a new series do I go with the elements from two movies that recently generated $450 million dollars plus each or do I continue on from the elements that general audiences were obviously tired of a decade ago, including a series that finished its run with less than two-million viewers a week (nevermind the fact that three out of four series had dwindling viewership numbers) and a movie that was a box-office bomb? I know which answer I give.