Because western society, especially the American flavor, sees every ad as sacrosanct and necessary for the planet to keep on spinning, while the mere suggestion that maybe we don't need billboards is met with disproportionate vitriol. I mean, someone elsewhere suggested that it would upend the economy if people couldn't shove their marketing copy in your face 24/7. Oh, imagine the horror!
Hacker News also has a, largely, American audience, so we ought not to pretend that we're not mostly talking about America and the west when we have these discussions. "But what about China?" I don't care, I don't live in China, most people here don't live in China. I have a laundry list of criticism of China, but something tells me we're not talking about China.