100 chapters of manga is not the same as 100 chapters of anime.
The medium are pretty different and if they were to animate all the source material and there wasn't a good stopping point, they have to make an original ending, practically sealing any possibility of future seasons or if the series has good sales, they would have to reboot the series or changing even more the source material.
Also you have to take in account the budget that every series has, the deadlines, the studio and others stuff, I read somewhere that 1 episode costs around 97.293USD to make and because anime runs on the so called committee which they are a bunch of companies putting the funds in order to create the anime, many of those just make it even to pay the committee and the profits after that depends on how much merchandise they can make of the series.
So yeah, I'm glad they stopped when they stopped, leave it open for a future season and hoping the sales are good enough to warrant a second season, if not I'll be satisfied with the season they gave us + the OVA.
If i want more there's the source material
Edit: I went and searched for anime episode costs and that is 11 million yen for a 30 minute episode so it's about 97.293 USD at the current exchange rate., so wanna to correct that XD