The vast majority of loans- basically every loan under $500,000 in most areas of the country, $750,000 in high cost areas, are bought by government-backed entities- Fannie Mae and Freddie Mac. They do the purchases at scale- hundreds of thousands of loans a month. See for instance the introduction to
https://www.fanniemae.com/resources/file/ir/pdf/quarterly-an...
What happens next is a very complex balancing act where some of the loans- mostly lower performing- are kept on Fannie's and Freddie's books, while others- mostly higher performing- are packaged into securities.
And again, what matters are the flows, not the values. The actual value of a property can be seen from auction/foreclosure sales, which are inevitably at a fraction of the prior sale price.
But Fannie/Freddie and holders of larger mortgages that are not performing manage the flow into foreclosure very carefully, in order to maintain prices and confidence.
This is a very, very complex machine. Maintaining values on one side and liquidity on the other is the purpose of this machine. I make no claims to deeply understanding it. I see the value of flows, of getting more commitments from people to feed their income into this machine, and see that reflected in the change in rates, and in the change in valuations. In terms of buying in- what is one buying into?
The other side of this argument is- what actually happens if someone is not able to make their payments? There seems also to be accumulating evidence that there is far more forgiveness for failing to pay a mortgage- even before COVID.
That all smells to me like a value bubble that pops when the end game for COVID is clear, with collateral damage for those who have commitments to flows for the long term but who may need to make changes in the short term.
Best wishes.