I will mention again, when you are picking a school as an athlete, you are picking a coach as much as anything else.
Q was not a good fit at KU. From the beginning of the season, Self had him basically out on the perimeter as a floor spacing shooter. When his shot was falling, that worked well. When it was not, it went poorly.
A couple of stat lines:
38-77, 49% from the field, 6-25, 24% from 3 PT, 3.3/1 Assist to Turnover ratio, 4 rebounds per game
106-276, 38% from the field, 54-159, 34% from 3 PT, 1/1 Assist to Turnover ratio, 2.5 rebounds per game
Those are both Quentin Grimes, both playing under Self. One was with team USA, where Q played on the ball quite a bit. The other is obviously Q playing at KU, where he played exclusively off the ball. You notice right away that at KU, 57% of Q's shots came from three, while for team USA, only about a third did. Q's primary role for KU was as a floor spacing shooter. He did okay in that role, but literally every other part of his game suffered as a result. At no point did we see the aggressive Grimes that you saw for Team USA, or in HS.
Self basically used Q as if he were Brannen Greene or Conner Frankamp. There is absolutely NO WAY a player with Grimes' skillset should have shot more than half his shots on the season from three. That's part of why KU was so hard to watch last year. The pieces never really fit together. Not enough shooting. Not enough floor spacing. Not enough creativity. I remember a few times early in the season where Q spotted a mismatch and ran into the post, where he called for the ball against a smaller player. That type of play disappeared as the season wore on, even though inverting the offense to let Dedric take a bigger player out to the perimeter where he had a skill advantage, and letting Q post a smaller player, where he had a size advantage was perhaps KU's best available MUA. We did not see that enough for whatever reason. Either way, it's water under the bridge now.
I just hope lessons were learned by everyone and that Self in particular has gotten more creative with how he will approach his sets this year with another team that may have some pieces that don't fit together very cleanly.