Berman and company tried to escape the brand name for a while. Star Trek wasn't even part of the show's title early on. Probably a mistake in retrospect.

There was a gap of mere months between the end of Voyager and the premiere of Enterprise. (Voyager actually shot an episode on some shiny new sets built for Enterprise.) Nemesis was also in the pipeline. Maybe there was too much Trek product at the time? It might have been better had the franchise taken a little vacation for a year or two. Disney ought to take heed as they prepare to saturate us with Star Wars.

Enterprise being on a fifth rate network that didn't even air in several key markets didn't help. (They had also lost some affiliates toward the end of Voyager's run.) And the Nielsen ratings didn't factor in how many people were downloading the show, since they couldn't see it where they lived. UPN fell apart not long after cancelling the show. Arguably, more people have seen reruns on Sci Fi than when it first aired.

That theme song didn't help much either. ;)