Interest rates are high. Maybe no one is willing to buy and renovate those lots because the cost of acquiring enough capital to do so is prohibitive.
There can be lots of reasons why houses sit vacant. I don’t think we should assume ill intent.
In large parts of Scandinavia there is an obligation to have residents in an apartment. The only legal reason not to have an apartment occupied is that it is for sale, or on the market for finding a renter (within the market price).
IMHO there is absolutely no reason to let units stay empty for any longer than what normal resident churn mandate.
But aside from Riverside it looks like buildings in the US West are used very efficiently