Except, in this case, we're talking about college players and it's actually the other way around. Yes, in most cases, they get free tuition and books, but the schools make huge money off of them and they are not compensated for it. I can't blame them for wanting to make sure they aren't injured just before making the jump to the pros, since it could significantly alter their career arc and their earnings.
In the case of the WHC, it's their club teams, not their country that has a ton invested in them. Most want to play for their country anyway, but refusing to go, is actually an act of loyalty to the people that pay their salaries, rather than disloyalty to their country.