Missing questions:

How often do you watch NFL games?
What do you believe the protests are about?
Do you believe in the cause of the protests?

Knowing the cause and goal of the protests are more important than the protest itself. The fact that so many said athletes shouldn't protest at all is an example of "you should be grateful" which is kind of the point of doing this so publicly. If they weren't an extremely small percentage of athletes that make it to the professional level, they can see themselves being potential victims of it.

In the end, if people are uninterested or uninformed on the subject of the protests, then it is proof that these should continue. The goal is to make people aware and empathetic to the increased danger of being killed in your home country by people sworn to protect and serve you. Until that happens, this probably won't stop.