Let me be that unwanted mooching uncle at every family party just this once, because yes, I admit I’ve contributed nothing to the manga industry aside from being a filthy scanlation reader. But someone please remind me why Japan is mass-producing already-written stories?
Short answer, cause that's what sells.
A not so long answer, Publisher want something they know would sell, Mangaka was forced either to make copy pasted story by their editor/publisher or their original one that aren't popular enough, budding mangaka saw what's on a lot of shelves and decide to join the wagon, adult/teen reader wants to know what's in the manga even before they read the synopsis or the first page so indirectly they encourage the long ass title, and the young teen reader wants fantasy like this (i remember the day where i almost exclusively read harem manga like Mahou Sensei Negima, Kami nomi zo shiru sekai, Sekirei, Sora no Otoshimono, etc. And yes, it's all harem ecchi action manga that basically have pretty similar plot though the case back then aren't as bad as the copy paste plot of today)
Only the talented story writer/manga artist that free from this current cycle.