I also think that "mobile entry" has had an impact. Not everyone has a smart phone and it's often older folks that have the discretionary income. It makes it less convenient to go and to dump tickets at the last minute. Or pick up tickets cheap at the last minute, which is what I used to do for Blue Jackets games if I had a free night. It was often easy to pick up a lower bowl ticket for $10-20 as a single.
That (and the fact that mobile entry doesn't always work well--if your phone's not set right, the scanner can have issues) and increased security add to hoops you need to jump thru to go, making it easier to sit home and watch on TV.
Also, the younger folks are not as invested in a specific team. They seem to have shorter attention spans--and will do what's fun at the moment more than the planning ahead required.
Then there's cost. That's one reason we gave up our PSU season tickets a few years ago. This is happening in other entertainment areas. The cheapest seats in Columbus for Genesis next month are over $200 if you add in fees.
But I do agree that COVID has been the biggest impact. That's why we didn't go to MLS Cup last year, though we could have, and did not go up for the Wisconsin game this fall, though we are using our season tickets for the Crew and Blue Jackets (though the latter is only a quarter-season pack).
And I do not discount the impact the political nonsense has had either--either side.