Okay, so who has done that?
He could also come back and just learn to be a great PG. That's as easy as adding eight percentage points to his average from three.
He came back this year and became a better defender, driver, finisher and teammate, and went undrafted.
So let's assume he comes back, improves again, and then what? Gets drafted 52nd? Still has to fight to make a roster with no guaranteed contract? At least now he has an extra year of earning power and can gain experience either in the D-League or overseas, where he can also improve as much or more than he could in a year at Kentucky with practice limits.
Since you posed the question. From this year's NBA first-round draft class alone:
1.
Willie Cauley-Stein. Willie wasn't getting drafted at #6 following his sophomore season, much less his freshman season. And that's the reason he returned each year.
2.
Frank Kaminsky. Nobody had heard of Kaminsky following his freshman and/or sophomore seasons, and he sure wasn't getting drafted at #9 following either of those seasons. He didn't get on the radar until his junior season. Kaminsky's return for his senior year was based upon his deliberate choice to earn his degree, make another run for a championship, and enjoy one last year of being in college.
3.
Sam Dekker. Dekker wasn't getting drafted following his freshman and/or sophomore years, much less getting drafted at #18.
4.
Jerian Grant. Grant wasn't getting drafted after his freshman or sophomore seasons, and he wasn't going in the first round following his junior season, much less at #19.
5.
Delon Wright. Wright wasn't getting drafted following his freshman or sophomore seasons of junior college. And he wasn't getting drafted in the first round following his junior season at Utah. He went #20 in this year's draft.
6.
Larry Nance. Nance wasn't getting drafted after his freshman or sophomore years. He likely still wasn't getting drafted following his junior year, much less at #27.
Let's face it, during their two seasons in Lexington neither of the Harrison twins were ever confused for tireless workers who were willing to make the changes or devote the hours to become elite players. One went in the middle of the second round. The other didn't get drafted. There were reasons for that.