I think a lot of the talent hoarding would decrease if promises had to kept for all four seasons.* Right now, an A+ prestige team can promise a top 10 recruit a start +15 minutes, play him for a year and then make him a backup the next year to another top 10 recruit that has been promised playing time. In real life, the sophomore isn't going to stand for that. He will transfer or jump to the pros.
With the teams that had nine players drafted, I bet all 9 of those guys were promised starts and minutes when they were recruited. Forcing the coach to keep those promises will end that in a hurry.
* The rule should be that the coach who makes the promise is required to keep it for four years, but a new coach does not have to keep the prior coach's promises.