This is pretty simple supply and demand and if you increase the supply, then prices will drop.
So, if I have 4,000 units and I let 100 stay empty to raise rents 8%, I win.
Rents aren’t chosen arbitrarily by the landlord. They can’t set to whatever they like, else they’d increase 100%.
This is different is a single landlord has a monopoly or there’s a cartel. But in a typical city there might be 500k units for rent. So if a landlord raises rent by 8% on their 4,000 units, then people will likely choose other units that didn’t go up.
Not to be dismissive, but this is basic econ101 and any intro text will have lots of examples and evidence of these principles at work.
I mean, you could write it as "better to have X% units empty instead of lowering rents by Y%, given Y >= X + Z, where Z is positive number determined by several factors" if you like
No, clearly not. Housing isn't a commodity and moving is a pain. If I offered you $10/month in a rent reduction (or off the mortgage if you own) to move across the street to an identical home, would you? How about saving $10/month in return for increasing your commute by 10 minutes a day?
Obviously, both of those become worth it at some level of savings. And decreasing rent by 0.05% to double the units occupied is worth it (probably). But there's a huge overlap in the middle where it's not clear what the effects will be, and that's where the real world is.
It's definitely true that things are more complicated in the real world, but that fact doesn't have-wave us into "Z is non-negative" territory.
That is, not only is Y=X a bad deal, but Y=X+Z is a bad deal for a good deal of positive Zs. Up to Zmax which is a positive value. For all values of Z < Zmax (including negative Zs) it's bad for JPM