I think the better way to phrase the question is:
Why did the show get canceled in season 4 when all of the other spin-offs had 7 seasons?
That offers the question without injecting your view of the people behind the show doing a "half assed job" (unless you were trying
to get a rise out of people).
Anyway, I'm sure someone will correct me if I'm wrong, but my guess would be the ratings had something to do with it. And why were the ratings so low? People who love the series will tell you there are lots of factors (like over-saturation of Trek, studio interference, and other reasons). People who hate the show will tell you it's because the show sucked (and some people who say the show sucked didn't even watch all of it, and they admit it on this board
)! And you know, it's kind of hard to blame its downfall on the series being lackluster when clearly the number of people tuning in for Trek was nosediving long before ENT. I would even argue that declining box office receipts for the TNG films contributed to the downfall of Trek on TV.
Anyway, here are the ratings for your analyzing pleasure:
And full disclosure: I enjoyed the series, and absolutely LOVED season 3!