I suppose money? As in sales and stuff, from what I remember the author asked help cause if sales of volume 2 weren't big it would get cancelled and end at volume 3? Something like that??? I'm not 100% sure. Sadly a loooooooot of series end really early, specially shoujo manga...So yeah,I guess since the series wasnt a big hit it wasn't worth keep going, at least in the eyes of the publisher. The author at least started a new series already, I hope this one is longer... I personally enjoy short stories but there's a difference in a story meant to be short and one forced to be.

AAAAAHHHH
THE AUTHOR GOTTA BE RAGEBAITING US (/TДT)/
It can't be the final chapter. I need at least 50 chapters!
I can tell the manga will get an anime!