It is sad that people buy too small cages for their buns, and it is primarily about ignorance I think. People think tthat if the pet-store sells a cage, it must be ok. It’s the same thing with bunny treats, lots of really unhealthy treats for bunnies are sold in pet stores, with a pic of a happy bunny on the package, and quite naturally, people believe it’s good stuff for bunnies. I did too, when I was a new bunny owner.
Where I live there are laws reagrding cage-size for bunnies depending on the size of the bun and there are also laws on how to furnish the insides of a cage. But in many countries it’s still ok to keep bunnies on net-flooring etc. I think awarness needs to be raised. Bunnies need space, and if a pet-owner-to-be thinks that’s impractical, and wants a small pet that can be kept in a cage all day, I think perhaps a hamster is a better option. (I don’t know anything about guinea-pigs but they might be a better option to).