The Marines still don't give bounties if you don't really do any crimes, and I wouldn't be shocked if they just straight up missed the minks being on the Roger crew. I don't think the Roger pirates were even known to fight anyone on their last voyage, and if Teach could be on Whitebeards ship for like 30 years, and have his own crew for a couple months without getting a bounty, I don't see why the minks couldn't go without getting one
we know Buggys bounty wasn't significantly high pre TS either iirc