Why don't we ever witness Mass Shooters and Murderers getting the Floyd treatment after committing their heinous crimes?

Most mass shooters are products of the MK Ultra program or its descendants. So the events are false flags. It is better if the patsy is killed outright so that there can be no way that he is ever interviewed by anyone who might recognise the psychological programming that has taken place.

Because they are white, armed, and often get arrested with a minor gunshot wound. Why not shoot George Floyd in the leg or shoulder?

Payback for fetishizing and raping White women. 

They're already having a "bad day".