Let's make something clear to all of the people shouting "Racism!" over Tim Tebow probably being signed by the Jaguars while Kaepernick is still out of the NFL: there's no evidence that that's the case.
First, look at Tim Tebow. Since his NFL career floundered, he went on to play baseball, then he devoted his time to becoming a commentator, and he's learned a new position for a shot at probably taking a pay cut to play as a backup tight end. For those of you who don't know much about football - no, making the transition from quarterback to tight end isn't easy. My assumption is that Tebow is going out of his way to carve a career path which is still devoted to football.
Now, with Kaepernick, who has basically been swimming in Nike money with his social justice activism front and center, it's not like he hasn't had opportunities to return to the game.
The AAF offered him a contract; but, the AAF's rule was that everybody get paid the same base salary with bonus opportunities linked to performance and popularity. Kaepernick turned them down because they wouldn't pay him $10 million more than any other player in the league.
The NFL literally has "End Racism" printed on the fields. I'm sure there are a dozen teams that would love to have him as a backup quarterback. Before my Bills picked up Trubisky I was arguing that we could use him as a backup in Buffalo. Hell, the Broncos, Eagles, Lions, Texans, and The Football Team are all in flux at the quarterback position and probably wouldn't mind having him start. Even the Saints might give him a shot at a starting position.
Most of the people who seem convinced that he was booted from the league entirely due to his political views don't seem to know how fickle the NFL is concerning talent, especially at the quarterback position. Jimmy Garoppolo lead the 49ers to a Super Bowl appearance a couple of years ago and the team just traded out of the first round of the draft for the next two years to get his replacement. Blake Bortles was basically the second coming and now he's on the Broncos' practice squad. Having a good year or two, as Kaepernick did, doesn't ensure job security. That comes with the territory of making millions of dollars a year to throw a ball.
Tebow clearly spent a ton of time and effort to prepare himself to backup a position that he didn't begin his career playing. Kaepernick clearly doesn't have that same desire to return to the game.