Lead generation for any site is hard, and in modern follower/feed based sites you're at the whims of the algorithm. It's worse in the adult industry where people don't have any "friend" mechanism to rebroadcast content.

The algorithms want to only show content that either makes money or builds followings, it's a feedback loop -- if you don't have followers/liked content then there's nothing for the algorithm to use to suggest your new content to new users based on, and your traffic dries up (source: I've worked on this style social media).

Posting in a broadcast style site like Reddit or Lemmy gets you exposure to a broader group without an algorithm meditating everything the user sees (less true of Reddit now). Ideally people look for content in a sub, like your content, click your bio for more, and see the links to paid sites and follow there.

It's an additional tool to gain a following, but also kinda required or else your account won't show up after a few days of starting. You could be Helen of Troy but never even get views on social media if you don't also do marketing for yourself.

To advertise paid for content. Have you not been paying any attention? Lemmy is small, and people who make money from NSFW content are incentivized to advertise on the biggest sites. TikTok and Instagram don't allow advertising, but Reddit and Twitter do. That's where sex workers rope in new subscribers.