I can only speak for my area (in California), but in many cases the properties are owned outright (no loan), and have their property taxes essentially fixed at

I can only speak for my area (in California), but in many cases the properties are owned outright (no loan), and have their property taxes essentially fixed at rates that were set decades ago due to Proposition 13, with only small adjustments thereafter. Therefore, the owners have little imperative to offer the properties for rent, with all the associated hassles, to meet their limited expenses. The properties are often poorly maintained for this reason. They can instead treat them as stores of value, which they might even be able to leverage into cash flows via other financial instruments. I think this is more the case for commercial properties than residential, but the problem exists to a degree in the residential market also.