Louis Rossmann has a semi-recent YT video exploring one hypothesis: landlords have mortgages that contain clauses in then which specify that if rents have to be a certain amount, and if they drop too much then that means the property value must have dropped.
* https://www.youtube.com/watch?v=NdfmMB1E_qk
And if the property value has dropped, perhaps bringing the mortgage closer to being underwater, then the bank may want the landowner to put more equity in it so that adds to the bank's cushion.
And landowners don't want to put more of their own money into a leveraged investment, so they'd rather just deal with the carrying costs rather than trigger an 'equity event'.
The hypothesis was originally put forward in a Reddit comment:
* https://www.reddit.com/r/nyc/comments/innhah/nearly_twothird...