Zoos don't make that much money from just entry fees. The wagons and expensive food stalls help fund them, along with the overprice souveniers. You are right though, unless a kid is disabled they should be walking and getting a little exercise. Do the places that encourage those annoying things have to pay extra liability insurance in case some unsuspecting person trips over them?
I was at the Calgary Zoo in 1999. They had really beautiful flowers and a big cat that had worn a dirt path pacing back and forth in front of his cage, he wanted out. It was sad. It is even more sad to think that someone would've been happy to shoot him to make a fur coat or a rug in front of the fireplace, so he was better off pacing, even if he didn't think so.
Zoos have gotten better in the US recently. In Philadelphia the zoo is very old and there isn't room to expand out-so they've expanded up. The animals have overhead walkways where they can move around above the humans. The new cat pens open onto each other where the cats are rotated into much larger areas. The whole thing makes for a unique experience, the cats seem happier with more room to explore.
San Diego has elephants. They don't have many elephants in northern zoos anymore, because they don't tolerate winter well, even when kept inside. It was a pleasure to see those huge beasts, especially now that the Chinese are fueling the mass elephant slaughters, due to their desire for ivory. Ivory looks so much better when worn by the elephants.