Experiance Laki, I kept one. The cage was about 450 square inches give of or take a few (of course my memory is not that good and it could have very well been bigger). Hand made from plywood and chicken wire. He never showed any sign of being unhappy and would joyfully gnaw on the block I put in there or the cage and eat his alfalfa. I had a harness for him and everything and even took him outside now and then to play in the yard on his leesh. But mostly let him play in my room. He was for all intensive purposes a happy bunny.
But I soon found out that as a kid I didn't have the patience or time to take care of him properly so I made the very hard decision to give him back to the store. It was hard but my school work was suffering because his gnawing at night was keeping me awake.
People tend to think they're right and I may be wrong but my dad is the one who built the cage, and he has had more experiance with little animals than me and quite a few people on here. Everything from gerbils, hamsters, rats, rabbits, and mice. So I would trust what he says.
I think what happens is it starts as one person doing this and then saying that their pet is extrememly happy and lived to a ripe old age, then people take to it. And it all snow balls from there. In the end they are rodents, call them anything else you want but most call them rodents. There are some facts about rodent that do not change no matter the rumor.
Rodents are incontinent, they will use the restroom everywhere.
They will hoard food.
They will gnaw on everything they can.
And they burrow, and thus do not mind small spaces. But this is where people get confused, as rodents cannot spend all of their time in a cramped space but only when at rest. Which is where the larger cage comes in, and this has to do with people. They don't want to spend as much time with their critter as would be otherwise required of them with a smaller cage. so I guess it really is a matter of how busy a person is as to how big the cage should be.
Now I'm not saying the cage should be tiny but it doesn't have to be like OMG a wall sized cage is all.
Whew that was a lot of typing, I hope I didn't come off as arrogant.