They are targetting whatever has eyeballs. If people are looking for purchasing advice they have probably come from Google. So if Google is indexing the subreddit it is fair game. That means every subreddit that is not 18+, and Reddit also forbids marking a subreddit as 18+ when the contents isn't really 18+ (as this was a form of mod protest a few years ago).

That number alone is a very good reason for the industry to target as much of it as they can / dare.

You say "sudreddit". Marketing teams say "self-selecting target segment".