CBT as a kink may be an evolutionary adaptation to protect men's most vulnerable (and evolutionarily useful) body part.
I have no idea why it's out there, but I suppose abusing it a bit may help toughen it up enough to ensure you can still have children when an accident happens.
Nah, CBT is just your good old Cock and Ball Torture. I don't think there is any evolutionary advantage, source: I've never seen any other species perform it (trust me I've looked). But I do think some men pay for it rather than paying for therapy so there's that.