hi @zvezda51 i really appreciate your thoughtful responses to me. i want to thank you by taking the time to write some good comments back because i looked over your posts and i believe you to be a thoughtful, caring person. if i didn't think that, i wouldn't waste my time here ;-)
Regarding longevity being an indicator of good care ... so that is not the issue here. the issue is that zoos are depressing because the animal is a prisoner. Just because a company can keep an animal alive for a long period of time may make it a better prison, but still a prison, and still depressing. For instance:

• At Seaworld aquariums, they have kept orcas alive for 20+ years in small "swimming pools", injecting them with steriods to make them "manageable", to perform tricks for paying audiences. This orca Kasatka was kept at SeaWorld for nearly 40 years. The article describes her open sores and fungal infections shortly before her death. Yes, there was longevity, but it was a long life of suffering and she had to perform up to 8 shows a day.
  https://www.independent.co.uk/news/world/americas/seaworld-killer-whale-dies-kasatka-orca-suffer-bacterial-infection-blackfish-10-years-florida-a7896956.html

By the way, would regular members of the public know if a hippo was "sick" or ill just by looking at it? Probably not.

• Tony the siberian bengal tiger was kept alive in a cage at the gas station as a roadside attraction for 17 years. Vets say that tigers live 14-18 years in captivity. He lived a "long" life but he lived at a gas station, breathing in truck fumes day and night. Many people say he suffered for 17 long years. https://www.bestofneworleans.com/thelatest/archives/2017/10/17/tony-the-truck-stop-tiger-euthanized-after-17-years-as-grosse-tete-attraction

i'll mention again that i am not attacking you personally, i think your intentions are lovely for posting this but it is important to understand that when people pay for-profit businesses to imprison animals for human convenience and entertainment, then those animals will continue to be imprisoned and it will be depressing. this is especially important for people who like animals, because they unintentionally pay to keep the animals locked up. traditional zoos have no place in modern society, but they will continue to stay in business if people think of them as "good".