You know he is only willing to play for some minimum amount of money? I don't know how anyone can say he isn't good enough to make a team. The Bears have Mark frickin Sanchez on the team. Kap is better than Sanchez any day. Having said that, he is not good enough to warrant putting up with the baggage he brings even is he offered to play for free.If he never took a knee and played the same he'd be out of the league. Check the contract situations of the guys you mentioned. Kap sucks at football. He's no more than another runner QB who gets figured out by the rest of the league (and maybe not even that: the first three years he started was the Harbaugh era in SF. As soon as Harbaugh left, Kap and the rest of the team sank back to their garbage-ity). He may have even been advised to start some kind of show in order to save his job - similar to that openly gay kid who found enough political sympathy to get drafted.
Even if we grant that QBR is the most important rating a QB can have, 23rd in the league isnt mediocre. Its back of the pack.
Also, if kneeling during the anthem was such a huge deal, why arent the owners cutting everyone - or at least way more players? Why are owners standing out there with their players? Its mostly a non issue. In the NFL its about winning.