You don't have long term sustained close quarter contact like you do with sporting events (3-4 hours of being crammed into stands like sardines).

Even without fans, you have a lot of close contact among the players. Especially the linemen.... over and over on every play. You have the players in huddles (when teams aren't doing no huddle). You have the sidelines (perhaps this could be mitigated by expanding the sideline from goalline to goalline). You have the locker rooms (I dunno if you've ever been in the home halftime locker room in Lane.... it's a little.... tight).

And even if you want to make the case that that's a loose case... you have the optics involved should something happen. You have the potential spread amongst the community. You have all the friends and family of those involved.

The long and short of it is, this is a lot different than some chance getting within 3-4 feet in the supermarket for 2 seconds.