There are a variety of factors that can affect housing prices, and the number of vacant homes is just one of them. Even though there are more than 20 million empty homes in the USA, there are still many people looking to buy or rent a home, which helps to keep demand for housing high. Additionally, housing prices are also affected by factors such as:

Economic conditions: A strong economy can lead to more people having the ability to afford to buy a home, which can drive up housing prices. Conversely, a weak economy can make it harder for people to afford to buy a home, which can cause housing prices to drop.

Interest rates: Low interest rates make it cheaper for people to borrow money to buy a home, which can drive up housing prices. High interest rates make it more expensive for people to borrow money, which can cause housing prices to drop.

Supply and demand: If there are more buyers than sellers, that can drive up housing prices. If there are more sellers than buyers, that can cause housing prices to drop.

Demographics: An aging population can lead to more people downsizing or selling their homes, which can cause housing prices to drop. A growing population can lead to more people looking to buy a home, which can drive up housing prices.

Location: Housing prices can vary greatly depending on where a home is located. Homes in desirable locations, such as close to good schools or in a popular city, can command a higher price than homes in less desirable locations.

It's also important to note that vacant homes in the USA are not evenly distributed across the country, certain areas may have a higher number of vacant homes but the overall housing market in those areas may not be affected.