Because sporting events and the United States are all about military power.
I am not going to get into the rightness or wrongness of it, but originally the NFL players were protesting what many people consider an absurd number of police shootings of unarmed Black men by bad cops with no indictments or convictions of those doing the shooting. Obviously, or at least it appears to me, that they are not protesting all police, but the ones doing the shootings.
For perhaps part of the last season of play, police officers got some backing from those who wanted to defend them even if that defense often lumped the good police officers in with the bad.
A blanket defense where it should have been more selective.
The only time we hear about the first responders is when they are responding to something spectacular while they are ignored for the rest of the time they are actually first responders or preventers.
We thank the military for their service, but not so much the police and fire fighters until there is a photo op moment and speeches can be made.
No this season, while the protest is still about the bad cops, the president decides to distract people from defending the good ones and changed everything once again to the military.
He finds the military a better pawn for his quest for adoration than the police.
He would not let the good police get any defense after only getting some during what was the last half of the last season.
People are now defending the flag and the military, and the police have been pushed out for the moment.