I think developing nations are aware of our techniques but do not wish to divert resources to using them.
"Come along now, you Chinese! Clean up that pollution from the Pearl River delta! It's irritating us in Hong Kong!" Oh it's real all right; I recollect slight breathing problems there - or perhaps it was the stuff we carried on the freighters.
Being one's brother's keeper is all very good but, if he wishes to sit downwind of his fire without a hard hat, then, well . . .
Good ideas on this thread but why don't the idiots who lead (insert country of choice) implement them? Fingers burnt in the past, political dogma, "You don't have the big picture." syndrome, too difficult, not invented here/by our party or just want to squander resources on a narrow group of political beneficiaries. Who knows?