While 80% of retirees in the US own their own home (and let's not pretend that 20% is a small number), slightly more than half of those homeowners haven't paid off their mortgage.
So, most retirees in the US still have to either pay rent or make mortgage payments.
A mortgage is far cheaper than rent. Even though that hypothetical cohort still has debts to pay, their cost of living is far more affordable than renting an equivalent place on the same spot.
Also, due to the ongoing rural-urban migration and gentrification, a house bought a couple of decades ago in the outskirts tends to be far more central and with far more benefits than those in the market right now with an equivalent cost.
I don't know the general stats of this at all. But of the people I personally know, their mortgage payments tend to be on par with what renting a comparable house would cost.
The financial advantage to buying vs renting isn't a smaller monthly bill, it's that you're building equity if you're buying.
In a few more years after that, inflation will have started to tilt the advantage substantially in favor of the mortgage over renting, as the latter can freely recalibrate to the market while the former is locked in at the time of signing.
The only downsides for mortgage versus rent are ongoing property taxes and upkeep, which are highly variable from one case to the next, but nowhere approach the cost of paying an equivalent amount of rent. And of course you have to discount equity as well.
I think what the OP meant is a mortgage that was initiated 15 to 20 years ago is far cheaper than rent today which is true.
of comparable size/desirability. The thing with a mortgage is, you're likely 'stuck' with the property you have, and so you may be stuck paying more money than you really need to pay. Likely if instead you just were renting, you could rent something far smaller with smaller payments, and be ahead.