From what I've seen watching two years of summer games, I think that many players are enjoying it, at least if they're playing well. I have been surprised by how many players have left before the end of the season, and by the fact that the teams (in good D1 and D1/juco leagues) have been scrabbling for rising college freshmen by the end of the season.
My son has loved his summer league experiences - his ideal life, having nothing to do but learn about and play baseball every day. However, he did leave early this summer, because he had more innings than expected in the college season, and his arm was done. I would hope that summer league teams don't blame the players for "me" attitudes when injuries or physical overuse happens. I would also think that they should expect it and manage for it.
I agree with old_school that maybe the "me" attitude is not all that surprising in some cases - I doubt players in the portal are having particularly good feelings about team loyalty.