It's a conspiracy...
He should have left with Brady. It was clear back then that he would need a couple of years to rebuild the team and don't forget Brady's last season with the Patriots was a disaster. The old Patriots had a great team. Brady, Gronk, Edelmann, Amendola, Mitchell, Hogan, Hightower, Chung, there were always great players in the team. Now they have nothing. That's likely due to their "we don't pay you well, we win SBs instead!" attitude.
They need to get their act together and get better players. It's no Bellichick, it's the team itself. It is his job to get the players though.
But this season seems to be a little odd, many good teams struggle, while otherwise performing very well. Cowboys, Bills, Chiefs, Dolphins. They all took losses or close games no one expected. Patriots almost won vs Eagles, that was a close one.