Football teams don't like distractions. And good olde Kap decided to make himself the Mother of all distractions. Training camp would have been a media, political and protesting circus. There's not one coach out there who's going to sign up for that, for a maybe backup QB.
this I can agree with and will add many in the hiring end of game didn't like the way he was protesting and wanted no part of him on their team.
As for lockerroom environment, some players strongly supported Colin, others agreed with his POV but didn't want to be involved, while other players strongly opposed the way he was protesting.
Coach's might have feared a divided lockeroom and that could affect the w-l column , making for another reason to sign less talented backups, but ones that would be accepted by the whole team .
Colin took a stance and paid for it.
He also refused to back down after seeing it was destroying his career.
That type of dedication, to a cause,needs to be commended.