Towards the end of Avatar, we see a lion turtle grant Aang the ability to energy bend. He telepathically says that he's the last of his kind. So at first, I thought maybe there was some natural disaster that wiped them all out, and then Legend of Korra came out where it was revealed there were hundreds of them. They were also fairly solitary.
Then it was revealed that the humans wiped them out. So how did the biggest creatures in the Avatar universe, able to support entire cities and ecosystems, allow themselves to be wiped out by people who they gave the bending to? even if they could throw lightning at it, I hardly think that would kill it. There were also flying ones( the lion turtles associated with air) and ones that could dive underwater. if this is that case why didn't they just fly heighter/ dive underwater?