There’s a whole vibrant industry of people you can pay to market whatever you want on Reddit. They can’t all be competing for the same few popular subreddits. They must be differentiated by targeting niche subreddits.
There are two different "ads" we're discussing here. One is the ads reddit the platform allows you to pay for, and it shows up in the client(s) as ads. Another is the type of ad where a company reaches out to community members and ask them to post about their project/product in exchange for a static sum, which looks like "normal posts" but are actually sponsored content.
The first one sucks for a multitude of reasons, the second one you basically don't notice are ads, yet they're all over reddit.
Can't say I know how it looks everywhere on reddit, as I'm not everywhere on reddit, but the AI subreddits I referenced earlier are filled with it, and I've even received offers myself to get paid to pay about stuff and I'm a nobody, so surely I only know of the surface.
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).
You can advertise on Reddit. If the return/cost ratio of industrialized astroturfing is better than ads then people will use it to promote their products.
