According to petpedia.co, about 80% of zoos abuse their animals whether it's on purpose or by accident and 96% of elephants in entertainment facilities are treated poorly.

Animals are taken from their homes to be put in small, stressful and very boring cages. These cages are sometimes not even cleaned the right way whether it's from waste filling their space or harmful chemicals being used to clean their area, etc.

Icanimal.org says that animals are removed from their natural habitats and social structures, they are confined to small, restrictive environments that deprive them of mental and physical stimulation. 

This is why zoos should be banned because of the negative impact on animals that are in captivity.  

In reality, most captive animals aren’t actually endangered. Specifically 18% of animals in zoos are actually endangered and are locked up. The main reason people keep animals captive is for money and show. 
Some examples are southern white rhinos, giant panda, the gray wolf, and much more.

Think about the animals, zoos will never have enough space for animals because animals are supposed to be free. Wild animals are wild. Imagine being put in a jail with a small area to sleep, awful meals, and only little or no free time throughout the day only to be watched for entertainment. Also, endangered animals aren’t supposed to be in zoos. 

The ‘surplus’ of animals or animals that are thriving at the moment are frequently killed even if they are healthy, making them endangered. In fact, more big cats are captive in America than roaming freely globally. 
Specifically 5,000 big cats are captive in the US and 3,900 aren't captive throughout the rest of the world.

They also have poor living conditions in artificial environments. 

Animals are treated poorly in zoos
Animals are meant to stay in their natural habitat endangered or not
Animals that aren't endangered are sometimes killed whether they are healthy or unhealthy

I found a poll on dailyedge.ie, only 16.6% of people said they think zoos are worth it. 

“The only creature in a zoo in its natural habitat is the Zoo keeper.” - Robert Brault.