Then why wasn't "Z" paid the bounty for turning himself in?
The bounty was to be paid to any black man or black men who could find and hold Zimmerman so he could undergo “justice” at the hands of the Black Panthers.
It can’t be relevant to wonder why Zimmerman wasn’t paid the bounty in return for surrendering to authorities.
As for turning himself in, he did so pursuant to being charged with second degree murder. Had he not complied with being taken into custody, he would have been a wanted fugiitive.
He had no choice, unless he wanted to try escaping to a country beyond the authorities’ jurisdiction.