I think the entire team and backroom staff lost their edge this season.
I'm sure part of it us psychological. Last season, especially with so many new faces, players had a point to prove and they battled their way to 2nd. This season, I think they lost a bit of drive and whether consciously or unconsciously suffered a bit of "after the Lord Mayor's show" effect.
Even successful teams with large budgets and frequent transfers can struggle to maintain a high level of performance, and without many fresh faces over the summer, we lost our focus.
No doubt a few players resting on their laurels this season too. At the time I thought McCall was a wee bit hasty in resigning, but looking back, think the timing was right for all concerned. It must have been pretty exhausting to try and sustain a level of success with decreasing resources. He might count himself a little unlucky he didn't get access to the new owners coffers, but probably better the new gaffer gets to play with that anyway.