“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.