I think the problem for "Trek" ultimately came down to, as the article hints, too much of it going on the air.

There was almost a 20 year gap between the original series and TNG. That gave the writers of the show 20 years of cultural change-and 20 years of new technology-to work with.

Since, TNG, however, the producers kept one version of Trek after another coming out, each mining the same themes over and over.