Have done it, but a lot of the suppositions about downsizing don't apply in many cases, I suspect.
For a start, most people who are still couples, and live in a nothing-special family home, would often have to move to a much cheaper area to make all the hassle worthwhile financially.
Most couples do not suddenly find an ordinary family home much too big for them, especially if they have dcs/gdcs visiting regularly - (like us).
The only couple I know who downsized before being widowed/becoming decrepit, moved from a large 5 bed 3 reception etc. and a very large garden - which was also in the middle of nowhere, so car needed for absolutely everything.
I also read of a fairly local couple, still far from ancient and perfectly fit, who moved from a large period family house selling for over £2m, to a very large new build flat with 2 balconies overlooking a Royal Park, which cost over £1m.
Anyone can see that that move was worthwhile, but not many of us will ever be in that sort of position. (They also got rid of their inconvenient dog, which made me hate them.)