The thread: https://old.reddit.com/r/manga/comments/bzg753/a_ton_of_scanlators_leaving_mangadex/

Background information for all you who are not mentally ill enough to know what the fuck is going on but mentally ill enough to care enough to read this huge boring blog post: Scanlation is a portmanteau of "scan" and "translation", basically scanlators are people acquire Japanese comic books (legally or illegally), translate them, edit them out, and then upload to the internet. It's a form of piracy and not exactly legal, although as far as I know some people (probably idiots) claim it's a grey zone and that it's okay to do it if the manga in question is not legally available in your area, but who really gives a fuck? It's something that started decades ago as a hobby but has since become a somewhat lucrative business for some people.

What usually happens is that scanlators generally prefer to have their own websites, where they can upload all their stuff, where they can get exposure to their site through popularity, ad revenue, have links to their patreons, etc. Of course, this is highly inconvenient for the fans, people who actually read manga. If you read like fifty different manga, and they're all translated by fifty different scanlation groups, do you want to visit all their sites one by one? Fuck no. You want an aggregator site where all that stuff will be posted. So then some smart people thought "You know what? I could make a site where I would pirate from the other pirates, and upload all their manga there, and make money myself from all the ad revenue! What are they gonna do about it, sue me?" and that's how you got sites like Kissmanga and a dozen other manga aggregator sites. Of course, this makes scanlators absolutely seethe about it, but it's not like they can do anything about it, and readers don't really give a fuck either way, they just go to those aggregator sites because it's more convenient for them.

Not all aggregator sites steal from thieves, though. Mangadex is an aggregator site that doesn't upload scanlations without the approval of scanlation groups themselves. They give them freedom in the sense that they let them upload, that they allow them to add credit pages and links to their own sites and patreons, and they allow them to add a delay to release of the new chapters to encourage people who can't wait to go read them on their own site. This is somewhat of a compromise solution that allows both scanlators to advertise and readers to have the convenience of reading everything on one place.

So what's all this fuss about, then? Well, you see, it turns out some people found out Mangadex wants to go legit one day. And this reminds people for Fakku and Crunchyroll. For those of you unfamiliar with these two, Fakku is a site that used to be an aggregator but for Japanese porn comics (the stuff ironic weebs call "hentai" and truweebs "eromanga"), and Crunchyroll the same but for anime (Japanese cartoons). Both of these sites used to be pirate aggregator sites like Mangadex, but once they got big enough, they started making deals with Japanese companies to publish stuff legally and eventually removed the illegal ("unlicensed" if you want to be a shithead about it) stuff from their sites. They used the fan translators as a stepping stone for financial success and kicked them out when they no longer needed them. So some scanlators started scaremongering about Mangadex planning to do the same, and decided to preemptively leave the site before it happens.

In response, Mangadex and their supporters are calling the scanlators leaving paranoid and accusing them of being greedy and only leaving because they want people to use their sites only and as proof of their claims posting an image that shows all the patreon accounts of all the scanlator groups that decided to leave in unison. In the long run, only people who will actually benefit from all this are aggregator sites like Kissmanga that don't give a fuck about scanlator consent and will just keep uploading like they always have, but will now get boosted traffic from people who used to read on Mangadex but can't be bothered to manually check out every single leaving scanlator's site.

TL;DR: Scanlators leaving Mangadex upon finding out Mangadex wants to go legit one day.