You really need to do some more research. First off, the kneeling started before Trump was elected. Secondly, in week 1 of the 2017 season, only 8 players either knelt, sat, or held fists in the air during the anthem. It was dying off until President Trump cast more light on the actions, which gave them the voice they were seeking. Third, most of these peaceful demonstrators are vocal about their cause year in/year out (such as Eric Reid, Malcolm Butler, & Michael Bennett). However, they're now being asked their reaction to the latest thing Trump has said on the subject, and that's all that makes the headlines (which seems to be all that you read).
Seriously, do your homework.