Because they have no idea of what they are doing. At best they are copying others but most likely they are afraid you will not be working without someone looking over your shoulder. A lot of times they do it as staging theater for investors (look at my team working in a cool hub) others to impressive customers (having an address in a locale is part of branding). No one does it for better ideas. Cheaper to fly everyone for a retreat if that was the case.

Becase the fund that invest on your startup does.

because the board members have leases nearby.

because someone that is invested want you to go there, spend money or create expenses (consume food from cafeteria,etc.)

If the student does not go in person to a university how valuable is the commercial lease at the university?