This is wildly incorrect. I volunteer at our local zoo. The animals there are given highly regulated diets that are tuned to their medical needs. They are stimulated often and receive plenty of exercise and care. This isn't the case for every zoo, but 95% of them operate this way.
Animals can be in zoos for many reasons. Many of them come to us due to sustaining injuries that would have otherwise killed them. Others come to us to avoid illegal poaching or the exotic pet trade. Others still come to us to participate in breeding programs that will, hopefully, accelerate that specie's repopulation. Zoos used to keep animals for entertainment but many of them are moving away from this model, and rightfully so.
This flagrant accusation was enough for me to stop reading.