I think it's because sometimes people took translation project from other site (where it was originally uploaded) without the scanlation team's permission, and upload them here on mangago.
There are some reason as to why some scanlation teams are very strict about not posting on mangago, one of them is to protect them from copyright strike. Posting translation to mangago could get them a higher risk of being caught for piracy (bcs this site is already notorious for it).
By posting and keeping it only on their site/account (like tumblr, discord, website, mangadex etc.), It'll be easier for them to manage and protect the fan-translations ┐(´ー`)┌
I know i should've talk about the comic but the credit about them hating mangago just make me confuse. Can someone explain to me why almost every uploader i've seen who upload on mdex always bitching on mangago??