> Probably obvious for many, but I didn't realize ACs don't transport any air into the room, but just moves it around

I had the same epiphany as you days after acquiring a CO2 monitor. Most people notice poor indoor air quality from proxies such as humidity and temperature. AC (without ventilation) eliminates these and tricks our senses very effectively, giving us cool and fresh feeling indoor spaces full of CO2 and devoid of oxygen.