Why do parents make their children swap bedrooms so much?

Growing up, most of my friends had 1 or 2 siblings. Some had as many as 4. Sometimes when I'd visit their houses they would suddenly annouce "oh btw I have sister 's bedroom now."

I myself have a sibling but we never had to swap rooms.

I can understand the premise of "it's fair - nobody has the 'better' room forever" or even "it keeps kids from getting bored of their room." But 1. none of my friends ever had an explanation for why they were made to do this back and forth, 2. Their siblings rooms were never particularly different in size or quality than their own room (this happened with like 4 different families for the record) and 3. It seems like a lot of effort to go to !

So I'm wondering, A) did anyone experience a lot of room-swapping while growing up? And B) what do you think the explanation is?