>>279720842
It's not the first time it happened, it was the same thing with the management of the alchemist. Though they release sales data and turns out the manga besides being a terrible adaptation is selling super well.

Also the series has long been finished in WN format, the LN isn't a 1:1 adaptation and has a lot of changes and seems to have changed a lot for volume 5 too.

Though as for why it got anime, I am pretty sure they got to the point they will adapt any fantasy series.