Even though former PSL users don't want to admit it, the development of the intellectual side of the blackpill owes a lot to the few good redpill, MRA, MGTOW and anti-feminist spaces that once existed. Those ~redpill guys had a few forums, but it was mostly individuals with anonymous websites and blogs stretching back to the late 1990s dot-com bubble. Eventually all of that converged into the r/TheRedPill subreddit, which reached its peak in popularity around 2010 - 2012, before it tapered off completely around 2015. The original popularisation of ideas about what the true nature of women is, and hypergamy was pretty much entirely the work of these groups.
If you want to check out what those guys were talking about, check out The Masculine Principle online book (the 2nd version released in 2015, not the original one from 2012), the NO MA'AM blog and the archive of the r/TheRedPill sidebar (that subreddit changed significantly over the years). It is also important to note that these particular redpill groups were very influenced by various old books, like "The Manipulated Man" from 1971 and so on.
As for the PSL forum users, they invented thins like the PSL looks scale, as well as many of the terms we use today (like "sub5" and "LTN", for example). Likewise, they adopted the incel term to describe themselves. As for the "incel" term specificially it doesn't come from some foid unlike what MSM would have you believe, the term has a long history:
https://incels.wiki/w/Incelosphere_timeline, and the particular "incel" abbreviation wasn't coined by that foid MSM touts up either, it comes from an anonymous user who interacted with her. Either way what these forum users contributed to the blackpill was largely the different kinds of experiences you will have depending on your looks. They also extended the discussion of things only being about relationships about women, to instead being about every facet of life, with ideas like genetic determinism.
When it comes to people like Andrew Tate, it's true that most users here don't come from his brand of second-wave PUA/redpill-grifting garbage, fans of his landed in places like Looksmax.org instead. I think a few might have found this place from semi-grifter second-wave redpillers, like the GamerGate guys who graduated to the Far Right and took that as far as they could, or potentially a few who got some of their information from people like Roosh V, Sam Hyde and hoe_math (basically people who repackaged old redpill or PUA ideas for zillenial and zoomer audiences).
The thing to remember about 4Chan is that it was originally founded as an anime forum. Due to this, and its anonymous and lightly moderated nature a particular type of anime fan would himself there. The type of lonely young zillenial and late millenial guys, who got bullied off sites like GameFAQs and Something Awful for not being tough enough, and for liking anime and anime/manga-artstyle games, and especially for feeling romantic and sexual affection towards anime girls.
On 4Chan they could all of a sudden freely engage in their favourite topic, without being criticised by a bunch of Gen X users obsessed with masculinity, and due to the lightly moderated nature of 4Chan they could discuss ecchi and hentai as well (porn). Eventually some giga-weaboo oldcels would come about and school all these young and impressionable 4Chan users on Japan's different target audience terms, and once they learned that their favourite anime genre of Cute Girls Doing Cute Things was apparently intended for adult young men, they allowed themselves to become dependent on it.
Whether it was due to crass jokes between users of how one could get the waifu of their dreams by "becoming" the waifu, people who were already troons and gays finding their way in, or increasingly degenerate nip ideas being tolerated and even celebrated (like outright troon characters, such as Bridget from Guilty Gear, Felix Argyle from Re: Zero and of course Astolfo from Fate/Apocrypha), the adjacent possible of becoming a troon had been established as a legitimate option for the incel-adjacent men there. Even though they might have spoken about stuff which could have landed them in places like this occasionally, their well was born poisoned and it continued to be poisoned over time.
The only ex-4Chan users here who hold proper blackpill beliefs either come from /pol/, or non-weeb or non-weeb-infested boards (whenever those might have existed). That's not to say that there aren't ex-4Chan weebs here, there are, and they effectively have their own subforum as well (The Sewers), where they talk about whatever they talk about. These are generally younger and newer users though, because the 4Chan users who could have been OGs on this site generally became troons instead, like I explained before.
