They aren’t stats, they are an example.
To put it in more relatable terms… If you get in a 30 minute line it’s very unlikely you’ll have to leave to use the restroom, for arguments sake maybe a 5% chance, double that to an hour and it becomes a little more likely put probably still rare, maybe 10%, add another half an hour to 1.5 hours and there’s a decent chance (20%) you’ll need the restroom, add another half hour to 2 hours and nearing half the people will likely need to step out to use the bathroom (40%), make it 2.5 hour and most people will likely need to step out to use the restroom, make it 3 hours and nearly everyone will need to step out of line to use the restroom at some point.
Those aren’t stats, just common sense examples.
The difference with disabilities is they often compound faster, instead of every half hour I randomly chose 10 minute increments for my example, depending on the disability it could be 5, 10, 15, 20, 25, etc.
The point is the same though, you were questioning why people that can wait in a short line can’t wait in a long line, that’s like me questioning why you can hold your bladder for 30 minutes but not 3 hours, the question makes no sense.