Kaepernick won't come here for the same reason he hasn't signed with any other team. He wants too much money to be a backup. Honestly, do you think he would sign a vet minimum contract at this point? No, he knows that he can make more money making Nike commercials. If he signs to be a backup with some team and then has to come in and actually perform, and he doesn't, then the narrative would be changed.
He is in a perfect place right now. The kid is still worth 20 million dollars (that was before the Nike contract) and he is relevant on the social stage. If he signed for a minimum contract he would just be a clipboard carrier. He won't do that unless he can make at least 5 mil a year.
Do you want to pay 5 million for a backup QB that may or may not be any better than what you have right now?