“Why is Colin Kaepernick still unsigned?”
That's not hard to answer. He
engaged in political grandstanding while on the job and wearing the
uniform of his employers. That's not a legally protected form of freedom
of speech. If you choose to do that sort of thing, there are likely to
be consequences. I know that if I did something like that I would have been sacked on the spot and quite correctly. This has nothing
to do with the correctness (or lack thereof) of the message he was
trying to communicate. It has to do with respect for your employers and
maintaining a professional deportment when you are on the clock and
wearing the company uniform. If you want to protest something, you do
it on your own time and in your own clothes.