The problem is that these don't fit into most Chinese apartment rentals. Landlords could make some big bank by installing an HVAC, but they are missing even in new buildings where 90sqm apartments are going for more than a million bucks.

Yep. My little apartment (400m²) in a low-rise in Canada, built just five years ago, has no in-unit ventilation whatsoever. If I want a cross-breeze (and I always want a cross-breeze), I have to open the outside windows and the door to the hallway, and let a ton of dust and pollen flow into the unit from outside. I have no idea who thought building an apartment building today like this made sense, but it seems to be a common perspective.

400 sqm is a "little" apartment? Sheesh, first-world problems :)