Exactly, and that's the difference. If he was a great player, teams would have no problem signing him. When you're a mediocre player, the play on the field isn't worth the baggage that comes along with you. Again, if it was Tom Brady, or pick a superstar black player for that matter, say, LeSean McCoy... it'd be a totally different story. When you're the absolute best at what you do, the teams will still sign you. When you're mediocre, it's just not worth it.
And I'd argue that for most (I'm sure there are a handful) it actually has very LITTLE to do with race, but the way he chose to protest. Kneeling for the national anthem. If he'd been out protesting in the community, alongside citizens, or protesting in another way, we wouldn't be having this conversation.
But your post generalized the people on this board as being racist... and that simply isn't the case. Are there a few? Sure. But that is a very low number.