It's a moot point and only relevant if you are never going to move again. Those is their 30's saying they have already paid off, or nearly, must have decided to never move again, which would be unusual.
We have moved 4 times, each time moving up the ladder. Our last move was at 38 years old, with a £350k mortgage, so we have been steadily paying that off, but won't finish until late 50's.
There has also been a very low interest rate for the recent years, when we were in our 20's in our first flat, the interest rate hit 15% for a while, and was around 10% for a long period, so we were never in a position to overpay, also we lost money on our second house due to the first house price crash.
We now have a lot of equity in this house, but we have moved to achieved this, have has huge mortgages, and paid a lot in mortgage payments although rarely been able to overpay.