Yeah some overnight trains can adjust their gauge on the France/Spain border.
On the China/Mongolia border on the other hand they disassemble the train, lift the train cars up one by one (with passengers inside), switch out the boogies and then reassemble. 3 hour process, you can fully sleep through it and not notice.
If it’s taking 3 hours on a passenger train, a 5-10 minute transfer seems vastly more efficient.
On a night train such as the Transsib that takes several days to get from A to B anyway, being able to sleep through it and not needing to lug your stuff around is usually considered more important.
(Although in some cases you are woken up for border formalities.)
Yes, but most people can't sleep through a train transfer