> having guaranteed quiet and privacy in the evenings are pretty huge.

That's a benefit for other roommates, not the landlord. Unless the roommates are the ones subleasing, which is a lot less common.

There is 0 incentive/benefit for the landlord to accept an uncommon arrangement for less money.

I wasn’t talking to landlords; I was talking to residents whose leases gave them the option to sublease.

Edited to add: I was also possibly talking to residents who were looking to sublease illegally. I didn’t ask.