Jamaal benefitted from being a 4 year starter, of which several came under Anae's GHGF offense, and with Ulu's size and as an RM, he wouldn't stick around if he was putting up those numbers, and would take his talents to the NFL.
Jamaal most likely would have gone pro after his JR year had he not injured his knee and needed to prove he was healthy, let alone his mom wanted him to graduate.