I don't really get this, because apparently this was the decision of the showrunners, it wasn't cancelled nor were there any indications it was in danger. I can get if some of the actors didn't want to be tied down to the show anymore, but again, I didn't see any indication any of the principal cast felt that way either.
The ending would have been fine if the show had been going on another season or 2, but given how the season went on, it felt like a very rushed ending. Eva barely felt like she was in the show this season, and having everyone split up the entire season just off. The Lily/Dorian storyline just abruptly stopped, Eva/Dracula storyline just abruptly stopped, and we only get a very slight reference to Mr. Hyde.
Just feels like moreso the showrunners were ready to quit. They had a ton of story left to tell.