Regarding the elephant controversy, I think a lot of it has to do with the fact that the zoo is owned by the City of Los Angeles and all big decisions have to go through the City Council. I remember that when Elephants of Asia opened there was a huge advertising campaign and ever since the elephants have been considered to be the zoo's star attractions. Although there is a very vocal group of animal activists trying to get Billy relocated to a sanctuary, the vast majority of Angelenos seem to want elephants at the zoo. I doubt that it would go over very well with the taxpayers to get rid of the elephant exhibit in favor of less flamboyant animals like deer or pigs.
It also must be remembered that there are some very pressing problems in Los Angeles right now (namely homelessness and crime) so the City Council is naturally focused on those areas. While some Zoo Chatters have made some excellent points about Billy not being able to breed and the lack of younger females, I think it all comes down to the Council being trapped between a rock and a hard place so to speak. They are politicians after all and are trying to please their constituents. Most Angelenos are rather uneducated about animal husbandry and all they really care about is having elephants at the zoo to show their kids. At the same time, the Council is already under pressure to relocate the exisiting elephants to a sanctuary so is unlikely to bring any new ones to the zoo.