It's a reason.
The main reason, IMO, was his steadfastness in force-fitting players to his scheme instead of the other way around. The first year was a hybrid, which was awful. The second year, it seemed, all facets of the defense for many games never seemed to click at once.
I do think if given another year, it could've gelled. But three 200-yard rushers, fan ire and so many meltdowns made it a no-brainer to fire him.
... And so off we go, once again, looking at the other shiny rocks across the stream (ooh, look at Lynn, look at Couglin!) with the exact same leadership as three other times before. Will the next rock do better, or just do some things better and some things worse, only to repeat the entire process again in two years if we don't make the playoffs by then? Or is the leadership the main part of the problem?