A lot of people are rethinking life and career due to Covid

Another opinion.
Kromer is a human being. This past year has been just brutal on a lot of people. It has also made many stop and think about life and career in general. Being a coach is all consuming. He may be burnt out and in need of a respite. Or he may wish to not coach again because of the extreme amount of hours and the toll it takes (and it doesn't start and end at the playing of games). Urban Meyer is a good example. He really struggled with trying to reconcile life and family with a football career and departed altogether for awhile.

Some of this will be answered if he makes a lateral move to another team.
But don't discount the California affect. It is quite real and I'm not meaning to be offensive to Californians (I was born and raised there). I'm merely saying that because Kromer is relatively highly compensated he loses a lot of his income to various taxes, and because of other factors unique to California like the enormous cost of housing (and especially the LA area), he might want to relocate to escape some of them as so many have and are.

Likely there was no single factor that caused this to happen. Things don't usually work that way.