Poor people are a tiny fraction compared to billionaires per capita.

But not in total. There are much more poor people than billionaires, and even if each billionaire produces 50 000x the emmisions that a poor person does, all in all the emmissions of poor people are quite relevant too.

(From an equality standpoint obviously billionaires should be emmission-capped or taxed to the point that they aren't billionaires anymore, there's no question about that. But poor people's emmissions are still significant and more than relevant to the climate.)