We learned the hard way: by people dying. They're trying to avoid a future people, who may have forgotten what we learned, from learning it the hard way. Again.
> Any life form advanced enough to be bothered by the effects of nuclear waste will presumably be capable of learning.
Lol what? Pick any mammal, they'll get destroyed by radiation poisoning but that doesn't mean they have the mental capacity to know why they're dying painful.
And no, the answer is not "a previous iteration of intelligent life left them dubious comics, sounds and symbols".
Any life form advanced enough to be bothered by the effects of nuclear waste will presumably be capable of learning.