Because hockey parents are absolutely insane. But I agree, you should let the kid know after the last game and before tryouts start.
A few years back an E9 team in NH had ( Squirts) tryouts the week before playoffs. Coach cut three or four of his kids and then wished them luck in the playoffs. To make matters worse, he was making offhanded comments in the locker room before and after the game that made it clear that those cut were already seen as second class citizens and not part of the team. Kids were teary eyed the whole weekend! What a guy!! Not great with kids but if you like skating around cones and being barked at from Sgt Hulka like you are Private Pyle, you can sign up for one of his skills camps. Only problem is you gotta go up to Maine... and as we all know, nobody goes to Maine for Hockey!!
Reminds me of a Sgt Hulka story from years ago. Kids were on a pretty good tournament team which he coached and the last day after try-outs he cut a couple pretty good kids (maybe Squirt Major or Peewee minor). One kid had multiple offers to go to a better program but Sgt Hulka promised him a spot so the kid turned down the offers. Now the kid was cut and the other team was all filled up so the parent called Sgt Hulka and said "WTF." Sgt Hulka explained to the dad, "I had to put this kid on because his dad put a roof on my dad's house last month, and I had to put this kid on so his younger brother would stay with the program, I had to put this kid on because he has been with the program since we started it..." and the list went on-and-on. Laughable.