Who wants to take the family to a ballpark that has a high probability of some sort of crime being perpetuated against them?
Druggers and muggers......where do I sign up for that?
Vilify the police and this is what happens.
There is certainly that aspect.
IMO, there is a also blend of local politics and local economics - see for instance, SF and Oakland. Both features negatively impacted the interest of sports audiences.
(It may be coincidence, but traditional communist countries never had national sports teams. Has California continued to deemphasize sports at the elementary school level as it did several decades ago?)
Add to that, of course, the COVID shutdown impacting those still interested.
A peak, in large measure, was the kneeling and its intimidation of coaches, owners and even public officials at both professional and college levels. That was an in-your-face experience for many in the national viewing audience
Much of that audience generally responded with a "FU, I will find my enjoyment in sports elsewhere".