Why Colin Kaepernick's On Cover Of TIME

TIME magazine says Colin Kaepernick is on the cover of their magazine 'cause the movement he sparked has gotten so huge ... and spread so far ... he was the obvious choice.

TMZ Sports asked TIME why it tapped Kaep for the latest cover, and a spokesperson told us the goal was exploring "the nationwide debate happening around national anthem protests."

The spokesperson added, the fact his protest has now become so widespread ... "from the rest of the NFL to high schools and colleges across the country" -- meant this was just the right time for a cover story.

Translation: He's gonna be gold for sales numbers.

The issue -- which hits newsstands Friday -- features a photograph of Colin Kaepernick taking a knee. It's a shot from one of his previous on-field protests, not a photo shoot.