I don't know if anyone has studied it, but I know why it exists

It's to sell higher quality ad slots. When a company goes to buy ads through AdSense, they get a ton of customization options. This one would be something like "avoid mentions of criminality". And a lot of companies just check that, because why not?

Companies do actually care about appearing next to NSFW stuff, because it "taints their image"

How much does it actually affect sales? Who knows, marketing has kind of lost the plot, and Google has been caught rampantly lying about conversion metrics and the ad slots themselves in all kinds of ways, so I don't think the data to answer that question actually exists