Might also have something to do about first jobs. Being in a single location helps form connections, find mentors and learn the culture (as in how to actually get stuff done) more easily than remote. Older employees already have that knowledge and can just do their own work fairly easily.

Might also be social as well - younger people are used to forming social circles with the people around them. Again, older employees are more likely to already have a social network outside of work, or family.