@Thenomain Not only making things easy for staff but also for players. It gives the game more focus. In my opinion when you have multiple sphere's the game gets diluted down and the stories are... tricky.
How do you reconcile what a werewolf can do, with what a vampire can do, with what a mage can do? What is challenging or difficult for one sphere is amazingly easy for the other and unfortunately it also makes it hard to shine and encourages massive optimization (I know, there will be those who do that anyway) in order to compete with the other splats.
As for the code? I am not as good a coder as you are. I freely admit that. So I like that in a single sphere I can focus on getting that /one/ thing right.