Well, if you frame the issue as humanity being imperiled, you kinda lose the misanthropic and psychopathic crowd, which is a significant percentage of the population. They might uh, hear that news and go: "Great! Population Zero, here we come!"

Whereas, the planet being unlivable, means they die too.

It's all about psychological framing.

Some people simply can't be compelled to care about anything except themselves (and nearest family / friend circle / insert object here). That's partially how we ended up in this mess in the first place: The Tragedy of the Commons.

Sorry to put it this way.