I do remember on some long rides when i was a kid and even later, especially if going to maybe sleep, as i've always been a bedwetter that I was in a diaper, and even as an adult there have been plenty of times i wore a diaper for long trips. I've done some solo flight from the US to EU with aerobatic single seat airplanes a few times, i always wore and brought with an extra couple diapers, as it's hours without anything available, and TBH using a urinal with a stick and a chute on in the airplane is not fun nor easy, and using a diaper is IMHO way safer, aerobatic airplanes are very touchy on the stick and NONE of them had an autopilot.
I know others that have and do the same thing, as especially if you happn to have say a shart or worse, that isnt going to be a good thing, cleaning a chute and then someone elses airplane after you have soiled it would not be fun nor easy to hide...be just a mess, pun intended.
Luckly i never had any issues with anything but pee on a flight solo but i know others that have.
Also, i know a friend that just said he wishes he had a diaper on when he was coming back from a colonoscopy, he eneded up with some serious cleaning and also tossing pants and underwear, more a bloodclot issues, but a diaper would have saved both the clothes and hs seat from some serious issues, he ended up getting a new seat from a junk yard in the end, as he didnt get it cleaned instantly and well, that was not the best choice.
But, really even with my ex's kids we let them wear or even suggested that they put on a pullup when we were going on long trips, i sorta required it on the airplane, as i flew us a lot places and just in my old C310, so no bathroom breaks and i'd hate to see a young kid trying to use a urinal on a small plane, that would be a disaster...I also required them to use thier carseats till they were too big to fit on the airplanes too, as that old bird just had lap belts in the back that were not that good and i know the kids were better and more comfortable in the old Britax Frontier carseats I had for them (went with a good quality for the car and the planes).
But really as a parent, having them put on a pullup was never an issue with them, and if they used it or not wasnt a big deal with me or the ex. it's just way better than cleanup in the car for sure.
Now, me i was a bedwetter so having one on me if i was going to sleep in the car was just normal...also my father was not one to stop often for a bathroom break either, so that said it was handy. and luckly in the 70's diaposables were a thing and i always (unless forgotten) had the old pampers fan fold diapers back then available, and used them at night till rather old actually, not sure if I was that small or just the diaper were bigger back then TBH
So, i really dont see why more parents dont just in case use the pulups that are easily available anywhere for the kids on all the longer trips, say longer than an hour or two for sure. it's just cheap insurance and when they get to the destination its easy for them to jsut toss in the trash when they goto the bathroom, not that big a deal as long as you as a parent make it not a big deal.
I also used to have the homeschooling kids over often, as i have a big house and lots of fun stuff and a farm to play on, even a private pond. But with the kids we didnt make them, but we strongly encourged them to use a pullup at night, and also when we did a few times take a few with us on a trip (Both in the plane and also van) would ask them to put on a pullup.
It wasnt ever that big a deal as it was everyone, no matter the age till adult, then they usually didnt travel with us much, but even the say 14yo's were if going on a 3hr plane ride to somelace (or longer as often would do the coast in one leg) would be asked to wear a pullup and i had them available, and i can only think of one time an older kid was a bit miffed, and i just said, no pullup, no comming with. and that was the end of it, which on a different trip (4 hours though) he ended up using the pullup in flight, but that was sorta expected at 4hours without stopping.