Cats in general have evolved to sleep for long periods to conserve energy for hunting. Big Cats will sleep for 17 - 18 hours before going on a hunt and modern house cats haven’t lost this need for rest. This is basically why cats get the zoomies periodically.

Not sure about cats and dogs specifically, but I can give a related answer. It’s been found that hibernating bears loose virtually no muscle mass and emerge with the same fitness they went to sleep with. They have some biological tricks that humans just don’t have, we are forced to exercise to maintain muscle. So maybe there’s similar effects in other animals, and we are just unlucky.

I think with dogs it’s mostly about not over feeding them. Then regular decent walks are enough for most breeds. Not my doggo though. 2x 1 hour walks a day with park play/chasing frisbee else he goes nuts in the house.

I think cats and dogs have a different muscle fibre profile than we do, they have a lot of quick muscles fibre, meant for the quick dashes of hunting prey, we have mostly slow muscle fibre , meant for marathons.

Maybe that has something to do with it. I’m not a vet. 🤷‍♀️ I just want to be able to sit on my arse like a cat. 😂

Dogs I can understand, especially since most of them need walking and are generally a bit more active. But cats??! Mfs sleeping for 20-22 hours a day. They must burn a lot when doing their 10 second zoomies.