why hasn´t this been updated?

Yeah, cuz there are 6 volumes thus far.

SIX?! WHERE?! Omg I wanna read this so much

Actually, there are 7 now. They're in Japanese, though. Here's the link: https://www.cmoa.jp/title/234291/
You'll have to buy them. I use Google Translate to understand it. The grammar is shit, but I can still comprehend it. The books aren't expensive since they're digital. If you (like me) are desperate to read them asap, I'd buy them.