"I mean this kind of thinking is a slippery slope to complacency that inevitably ends with "why ski at all"?"
or this line of thinking keeps you from making a pair of expensive waterproof pants no longer waterproof.
I am asking honestly- how often do you change lenses during your ski day, and is getting back to a lodge/ parking not possible?
Depends on the weather. There are days when it's blue bird all around or cloudy all around or mixed or whiteout and many configurations in between.
I can't predit the weather when I go to a resort, so I cannot tell you how many times I have swapped out. Yeah some days, the weather doesn't change much from the forecast, so I definitely have not swapped out the forecast lens. But variable weather happens a lot too that I've swapped out especially during mid-day and afternoon when clouds seem to clear.
I can tell you this much on night skiing days I would start mid-day or afternoon and hit the après then go back to the slopes for night skiing and swap to low-light/night lens, so that's definitely a two-lens day.
Not all people ski in and out of their lodge or park their car near the resort that they can just swap out stuff from the room or the car. Some skiing areas necessitates that you carry stuff on your person.