There is a big difference in keeping orcas and keeping other animals. Orcas can swim 100 miles a day and would need to swim 1,208 laps in their tanks to equal that. Other animals are much smaller than the orca and the environment they are kept in at zoos are proportionally a lot larger for them than the orcas (usually - there are bad zoos in the world but in the past 10/20 years most zoos have been accommodating larger exhibits).