Or the buyer is a long-time homeowner who has largely paid off the mortgage on their original residence, or at least paid it down such that inflation + payments has increased their home equity to near the purchase price of a new home.

This includes nearly all senior citizen purchases, but it's also a surprising number of 40/50-something wage earners who bought in HCOL areas around 2010, saw their $800K homes appreciate to about $2M, have paid the mortgage down to about $450K (or paid it off entirely, using stock price appreciation), and also have a couple million in appreciated stocks from saving abundantly during the 00s and 10s and enjoying the stock price appreciation.