[Tade0]

Bear in mind that in space exercise is mandatory, because the lack of it considerably reduces the time a given person can spend there, which in turn would require more frequent launches, which are expensive.

Also - they're the best of the best. They sort of earned the privilege of not doing overtime.

[CodeCube]

Also, let's not forget that overworking them has literally led to a "mutiny" in space before ;) https://en.wikipedia.org/wiki/Skylab_mutiny