Kaepernick’s career was going downhill before he started protesting. He was already the backup by then and frankly already had a reputation as an egotistical jackass. If you want to be an egotistical jackass in the NFL, it’s possible, but it will limit your career options even if you have the talent to back them up, which Kaep didn’t at the end. He’s also went on to sabotage his own comeback opportunities at least once. Probably the best comparison I could make is Kyrie Irving, and the only reason Kyrie isn’t out of the league is the NBA CBA.