There were a few problems with Enterprise:
-The UPN executives made a bunch of bad moves that alienated the fans and compromised the show: the Akiraprise, mandating the Temporal Cold War so the show was both a prequel and sequel, keeping the tech mostly the same, etc...
-A tapped out writing staff who weren't writing the stories they wanted to write and were forced to keep the TNG formula.
-Berman staying and refusing to shake up the directing and soundtracks, which made the shows seem even blander than their scripts did.
-Fans being burnt out after a decade of Trek shows and what was perceived to be declining quality.
If Enterprise had been something special or at least gave the audience the impression that they were trying to make a great program, people might've given the show the benefit of the doubt in those first two seasons. Sadly, things didn't work out that way and the franchise wound up languishing for a while.