I think entertainers got gassed from seeing athletes say whatever they want with no consequences.
What they don't take into account is that, for an athlete, if you can perform at a high level and win games you can get away with a lot. There's not a lot of high level athletes compared to the general population. If Colin Kaepernick was a 4000 yard a season passer or a Mike Vick level 2800 yards passing with 1000 yards rushing, he'd still be in the league whether he took a knee or not.
As far as entertainers go, there are a million other hungry artists waiting to take their spot who are more than willing to shut up and not alienate potential customers.