Well, Kaepernick's passwer rating last year was better than 13 other starting quarterbacks. That makes him mediocre but those 13 worse QB's still have jobs, including Eli Manning and Cam Newton. Kaepernick was cut because he just wasn't getting it done on the field for the 49ers. That's the main reason he's not getting a job but it's also reasonable to believe that the political stuff has something to do with it too, at least a little.
Why would anyone take a risk hiring a mediocre quarterback who infamously stepped on America? If I'm a team owner I wouldn't hire him.
He certainly comes with some baggage and I would think most teams would not want that sort of baggage.
I'm mildly interested to see his playing time and completions/attempts compared to Manning. I would guess Manning's was a tad higher. Newton as well, but he has ego baggage that I would not want on my team, that is, if I were a billionaire and owned a team.