Every TV show has episodes that viewers don't care for. I have never heard of a lame episode being the reason a show got canned.
A much more important factor was the alleged "network" airing
Enterprise, UPN. The network didn't have enough markets to cover the the US, so the show was not even available to watch in some locations. UPN's target demographic did not match the likely viewers for the show. Also,
Enterprise was often pre-empted for sporting events, and was poorly advertised; Bakula has said in interviews that there are plenty of people who were not even aware he starred in a TV series that ran for four years.
Add to this the shrinking TV audience at the time, the migration to cable TV, UPN's imminent collapse, and TiVO numbers not being used to analyze a show's success. I believe I read somewhere (so sorry that I can't remember where

) something about
Enterprise being a top-25 TiVO show in its last season. Perhaps someone else has more info about this.
Finally, at the time someone with power (i.e., a studio or network executive) was really needed to go to bat for the show, no one stepped up, for all sorts of reasons that didn't have a whole lot to do with the quality of this or that episode. Remember the first year of
The X-Files? Fox (both studio and network) stuck with the show despite dismal ratings its first season, advertised the hell out of it, aired five-day marathons during that first summer to get people to sample the show-- and it survived to became a flagship series for the network.
Bottom line: The studio wants to make back its investment in the production, and the network wants to sell soap, as they used to say. How many shows do you see on TV that are crap, but have acceptable ratings and just keep coming back every new season like a bad penny? How many shows have you seen that are critical darlings, beautifully written and made, but they don't last three months because their ratings aren't good enough? It all comes down to money.