they have almost succeeded in closing down Sea World ... among other crazy things they have going.
PETA is crazy, but they don't deserve credit for closing Sea World or zoos or anything else. Sea World keeps whales in tanks that can't really house them, there was a documentary about it, and people (myself included) don't go there. They are trying to keep up by changing towards a more thrill ride centric park, but they can't keep up with their competition.
You're giving way too much credit to PETA, which is an organization that makes headlines by being nuts, but has no real pull with the average person.
Sea World is failing because of capitalism. With HD nature shows on demand on Netflix and all kinds of oddities on YouTube so many other opportunities to do fun stuff in the state, kids don't give a shit about seeing a whale in a tank, or a bear riding a unicycle or whatever else.