Poppa Joe put Hunter out there because he was damaged goods and expendable. Do the math - how much hookers and blow could one guy do? He couldn't make a dent in the cash that was being gobbled up in this racket.
Ole Joe probably figured Hunter would do himself in, and he likely had beat the kid when he was younger, or just as bad, did a psyche number on him. Poppa Joe has a temper and is NOT an amicable guy. Likely he felt Hunter was going to take the wrap since he had bailed him out so much previously - he OWED Poppa Joe everything, and you can bet Ole Joe was constantly squeezing and reinforcing that.
Just some thoughts -