He wasn't re-signed because he didn't fit the system the next coach wanted to run.
And no one else wanted a QB with a steadily declining QBR with a bad attitude.
But no one stopped him from voicing his opinion ever.
Also, people forget that this all started with him sitting on the bench during the anthem after learning he wouldn't start a preseason game. When people complained about his disrespectful behavior, he turned it into a racial thing. Yet, he was still given 10 games of opportunity as the starter.