The Wizard of Oz was one of the absolute most dangerous films ever made. OP is there a good essay about the history of this? It's a REALLY fascinating story and a lot of people who watch and enjoy movies would probably be absorbed into reading it.
I think I looked this up at one point, and weirdly, none of them died from the asbestos. I seem to remember several of the actors died relatively young, so maybe something else got them first.
Asbestos isn't that bad for you when compared to heavy amphetamine and barbiturate use. But I'm sure it did help with the emotional pain of being constantly molested and likely raped or being poisoned to death from toxic paint on your face.
It was in 1939. Asbestos usually fucks you 20 years later, so around 1950. While Asbestos related diseases were acknowledged in the 40s, the widespread understanding of a health hazard was only coming up in the 60s to 80s.
So it is very well possible, that it simply wasn't checked.
Just goes to show you Hollywood was always a messed up place. It was indifferent to people back then, it is indifferent to people now.
On a slightly related topic, "Babylon" was too much the same self loathing and despair from Hollywood; it ultimately bombed, despite being a technically great movie, because everyone is sick and tired of seeing Hollywood bemoaning that this messed up world is never going to change.
I hope they will be proven wrong after the strike.