The network execs may be at fault for not letting Voyager and Enterprise be the shows they were supposed to be, but you can't blame them for all the shitty scripts that plagued both shows.
I doubt the network execs told them: "Make 5 time travel episodes a season", or "Make the temporal cold war absurdly convoluted, and not in a mysterious exciting Lost or Twin Peaks sense, but rather in a 'Just fucking stupid and impossible to logically track' sense."
They could have made a much better show with more serialized arcs. They could have made a much better show with an episodic 25th century show. But with such low standards for scripts, they could have never produced anything anyone liked.
Between the end of DS9 and the 3rd season of Enterprise, both the execs and the writers displayed absolutely no idea what the people who still tuned in every week wanted in a television show. The execs thought they wanted the same repetitive predictable drivel you see on a show like Full House, and the writers thought they wanted rehashes of successful TNG tropes. None of them ever thought 'Hey, let's have a character driven show with exciting adventure and smart action', which is what might have kept the franchise going a little longer.