Stuff like that does matter more to a competitive athlete than it does to a regular person. There's a reason whenever they are flat it's the entire team. It's not like they all decided at the same time to be lazy.
It's also not about being tired, they're still flying out there, much faster than fresh AHL players. They are just slightly more tired than the other team, and that's a disadvantage that has to be overcome, regardless of whether it qualifies as a valid excuse for losing.
My philosophy is there's no sense stressing over stuff you can't control. On to the next game.