@AlphaInsaiyan ok, i'll try to explain. First, you need to know this:
1) unauthorized translating & scanlating manga is illegal. Almost every manga you read online is a product of crime. Including this and many more.
2) it is considered illegal, but it does help in popularizing the Japanese culture. So, many publishers just turn their eyes and let it go. Not officially approve it, not actively take it down either.
3) many fans do it for almost 0 profit just because they like doing it. And want other people to like what they do. To share the joy is a form of joy itself.
4) so much manga translated, so much group made it. It is inconvenient for us (reader) to open each group website just to read 1 manga, and open another website for another manga. Hence, come the "compiler" site. The 1 website as a portal where you can read all kind of manga from all kind of group translation/scanlation.
5) Almost all of the compiler is aggregator. They take another group hardwork and put them in their website without approval and clear profit sharing policy (almost all aggregator website earn money from ads). The aggregator earn money from other's hardwork without permission nor sharing the profit. SHAME ON THEM.
6) Mangadex is not aggregator. I don't know everything in detail, but any manga uploaded in this website has approval from the group. So many policy. I don't know about profit sharing, tho. Is this even gain any profit?
Okay, the problem with JB (Jaiminis Box) is, they dont want to put their work in Mangadex. Just that. Mangadex, as gentlemanly it is, just can't snatch it without the group's approval like some shameless aggregator site.
I don't know what their motive is. Are they have some clash with the admins? Are they overconfident with their skill & trust too much in their own website visitor? Did they do it to gain more profit (its their website, they free to put on Google ads, or anything in there. Not like "No ads policy" in Mangadex)? I dont know. Ask them yourself. Hope this help.