Because under Poch it wasn't dull winning football I imagine. Because Poch had 5 years sculpting us into a dour side that wasn't even winning football matches anymore? Performances under him had been poor for over a year, it was always going to reach a breaking point where either we would gain some form with the wins, or the winning would give way to defeats and draws that the performances deserved. Unfortunately it was the latter.
I'd also imagine that Mourinho will reach a similar crossroads himself, but he deserves some slack whilst he familiarises himself with the squad and has chance to tweak it over a few windows, bybtge beginning of next season we should be in a better position to judge.