Trump isn't perpetuating it by reacting to it, the players are by kneeling.
I want you to think about something.
Every time a liberal (or some RINO or w/e) says "you can't do (x), it's wrong!"
You cheer like *** mad when Trump does it.
Do you understand how this applies both ways?
Trump tries to tell them what to do, they say "*** you, I'm doing it anyway."
It's a human response. To quote the troubadours of anger against the mechanical devices, "*** you, I won't do what you tell me."