“Investors” (big, small, whatever) are selling homes at those prices (or renting, or VRBOing) because there are customers ready to buy the next available unit.
The “investors” are the buyers/customers, and they aren’t reselling these houses–they’re renting them out. It’s mostly corporations increasingly doing over the last 15 years or so (I think it started around the 2008 financial crisis). They have the capital to do it and so regular people are being priced out more and more as this practice keeps driving up prices.
It didn’t used to be this way. Even in my “cheap” area, when I bought my house back in 2005 all but one house on my block were owner-occupied. Now, more than half the houses are rentals because whenever one came up for sale it was bought by a rental company. This is a serious crisis that needs to be addressed.
Renting them out is not selling, it’s an ongoing income source for the owner. The renter does not determine the price when the alternative is to move elsewhere or live out of your car. There’s simply not enough housing–supply is limited. It’s not a simple equation like a factory adjusting the output and price of its widgets. If things were as simple as you say, there wouldn’t be such a severe housing crisis in the US. Just search for US housing crisis, there are thousands of articles explaining what’s going on.