I think a lot of it boils down to the fact that college kids can't stand their summer leagues. It's not a knock on the guys who run them either, but it's hard to convince a kid to care about a bunch of strangers who also don't want to be there. Broke college kids, let me add that in. You take a bunch of college kids with no money, have them live with strangers and have them compete in a league where maybe 4 kids get drafted in any given year and they're supposed to care/get excited to go the park everyday?
It gets old after a while. At school they're working and struggling next to the same people everyday working towards a common goal. With summer ball they're having their summer, their only time off, taken from them - playing in wildly different atmosphere with stakes not nearly as great as what they're accustomed to. It's hard to get up for those games. The only silver lining is they may get drafted but there are only a handful of leagues that produce multiple draft picks every season.
Don't forget, they're also living in a world where social media exists. They can see what their friends are up to 24/7. You think they want to be sitting on a 6 hour bus ride when a few girls from campus are having a party at the lake house? Ask a player if he'd rather win a summer league championship or spend his entire summer at the lake, making money, doing whatever and see what they say.
I have two in leagues. One in a decent league, the other in a local league. From going to games, talking to players, and sitting behind the dugout and getting the mic'd up version. 95% of those kids do not want to be there, and sometimes the coaching staff. There are college baseball social media pages where you see the summer ball experience from the players side. There is a theme.
Regardless, that is no excuse for any of them to be rude or ungrateful. That is pretty unfortunate.