I would have been fine with season four being the last one if that's what the producers intended, but the fact that Starz cancelled it after the season was done filming and publicly announced it before it premiered killed off a lot of hype.
I don't know why we still live in a world where shows get cancelled at the last minute. If a network is planning to end the series, at least let the writers and producers know ahead of time so they can figure out a proper ending. The Goldbergs was cancelled after season ten was done filming, the iCarly reboot ended on a cliffhanger because it was cancelled. At least in the case of Mom, CBS cancelled it while season eight was still filming, but they had to rush to come up with an ending because it was later on in the season when they found out.