LOL. Think like a ball.
Female...
Most days. Let me see how little I can do today and how small a place I can fit my gigantic butt into.
After dark. Food guy is in the room. See if he has rat. Nope. Go back to sleep.
10% let me out to play.
Another 10%. Leave me alone. I don't like you.
Males...
Daytime. Sleep.
Nighttime. I know this is the thousandth time I have tried, but maybe this time I can find a way to get to that girls tub.
Comes to front of tub, you going to let me go on a date tonight?
80%. Stop trying to feed me you know I only eat six months out of the year.
All...
Oh wow! Poop! Let me see if I can paint a picture.
To the OP. There are reasons beyond just saving space that breeders keep balls like this.
The biggest being it is super easy to keep the animals content, healthy, and "happy" with minimal maintenance.