I'm not sure I'd call what KenPom does a "model". The only thing "subjective" that he does is adjust for opponent and tempo. You could call that a "model", I suppose, but I imagine he has a literal ton of empirical data to back that up. I'd be curious how much these adjustments even affect the overall ratings, honestly.It doesn't have to be nefarious to be a glitch in the model.
I work with a lot of models in my job, and most of them have implicit guardrails that tend to influence the model's interpretation of new data, i.e. the model's starting point never gets completely removed from the model. I also find that models frequently equally weight data, including outliers. I imagine this is unavoidable with a model based on per possession efficiency, which is fine for measuring offense and defense, but can skew outcomes when looking at the team as a whole.
By focusing on efficiency, KenPom has to be leaving the margin uncapped, even if the model is adjusting for quality of opponents. There is no other way to incorporate efficiency with a capped margin because how would the model know which possessions to throw out?
Our defense has not been impressive this year. Combine that with a lot of teams that played very well on offense, keyed up to play the 2 time defending champs.