They can, but why would they? They're probably busy, possibly with family. These aren't graduates desperate for a job, if they're the ideal employee you're looking for they'll have a comfortable fallback in continuing what they're doing and plenty of other companies that don't want them to do homework.
What if 9 great companies give just 2 hours of homework and 1 gives none?
What if 9 great companies give just 2 hours of homework and 1 gives none?