People used to die of Cholera in London because they were drinking sewer water. There were so many deaths that they were motivated to fix this.

We still breathe sewer air. There weren't enough pandemic deaths to motivate us to fix this.

Proper ventilation gets CO2 levels down below 500ppm, at which point all respiratory illness transmission rates approach zero. CO2 is a proxy for how well our exhales are clearing the room before other people inhale.

What makes fixing this expensive is that one doesn't want to trade energy use for clean air. Modern heat exchange technologies require more space than old building support without modification.

There has been much written about this. Here is one article:

https://www.theatlantic.com/health/archive/2021/09/coronavir...