This is an interesting point that I’ve seen play out as you described. It was the parents of an acquaintance of mine, and they did choose the downsize option because they were getting too old for the upkeep of a whole house and niceties it brings such as having the hotel like amenities of a doorman. Then there’s the point of choosing new vs. old stock, agreed there is a higher demand, thus it demands higher cost.
Further - because it’s easy & cheap to stay in a paid off SFH indefinitely, a lot of retirees do so.
Part of it is inertia and part of it is stuff like “where will the grandkids stay if I moved to a condo”.
Which sure if your monthly costs are near $0 then having 2-3 spare bedrooms sit empty 360 days per year seems sensible.
If they could cash out 50% of their homes value and have same/lower monthlies, then losing some spare bedrooms wouldn’t matter.
Downgrading has to be both easy and cost saving for retirees to do it.
Between my dad and his 3 siblings only 1 has done the downgrade-after-70 thing. And even then that aunt only did so as a gift to her son selling them the family home below market …