I guess my question is whether the bottom 1/4 knew in advance they were the bottom 1/4 and were at risk? You may say they should have known, but denial is a strong defense mechanism. Would coaches ever take players (or parents) aside far in advance and say, "Hey, things aren't looking great, and if they don't improve, you may not be asked back to join the team next year?" And if not, why not? Do you think some communication would be seen as straightforward or as disrespectful? I, as a parent, would appreciate the heads-up, but others' mileage may vary.
We would usually "encourage" players in the bottom 1/4 to attend multiple tryouts...