I wasn't a fan of Enterprise and still am not. What killed Enterprise was UPN moving it to the infamous Friday Night Death Slot. However some shows survive and kick ass in the Death Slot, Stargate SG-1 fro example, Atlantis, Law & Order SVU, Monk... so many.
ENT being moved to Friday nights wasn't what killed the show although its clear the new timeslot didn't help. The show was pretty much dead on arrival at that time slot.
Paramount's parent company, CBS, had let it be known that the decision that season 4 would be ENT's last, hell, Star Trek's last, al least for the foreseeable future, had been made before
the move to Friday nights.
And if I recall correctly, and I may not, ENT's Friday night ratings were at least the equal of the Stargates (or pretty close). L&O and Monk of course, are entirely different animals.