Because of the massive summer time melting of the Arctic ice sheet, the polar bears have been having a very hard time as of late. They rely on a the ice pack to hunt seals, without the floating ice they are forced to swim for miles to even find some place to rest. This often means that they starve to death, or because of exhaustion drown.
Many people estimate that 2/3’s of the wild population could be gone in as little as 50 years. But putting them on the endangered species list mean that they would be the first species put on the list specifically because of global warming. This presents a problem to an administration that has gone out of its way to deny that global warming is a problem, and only recently admitted it was real! What is a denier to do? If they put the polar bear on the list then that means they are bound legally to do something about global warming, or perhaps that they could be sued for not doing something.
So of course when Greenpeace showed up in a polar bear suite to protest this lack of action, they were promptly arrested.