When the occupancy rate is high across the market, purposely withholding units by using higher than market-rate prices across a large enough percentage of the m

When the occupancy rate is high across the market, purposely withholding units by using higher than market-rate prices across a large enough percentage of the market artificially inflates the prices. "Large enough" doesn't need to be anywhere near a majority of the market to impact the entire market. There's no competitive advantage to using a lower rate, because the unit is likely to get rented either way. You cannot look at the entire US. You have to look market by market. It's not price fixing across the entire US, but it's absolutely price fixing in particular markets.