As other's have pointed out, they probably think AI will pay them more than even ads. Or, since they want to IPO and cash out, they are betting, with the current hype around "AI", that public markets will value AI high enough to value "possible" data sources of AI highly.
From the post:
> Me: "Because I assume the majority of it isn't server costs. I assume the majority is the opportunity cost per user."
> Reddit: "Exactly.""
Reddit's doesn't care about the $0.12, they care about the ads that doesn't get shown.