A larger demographic means a lot more people enjoy it means more profit.
However, it is not always about money. I think Sony knew about how popular Ghostbusters is and realized that they would profit more by opening the demographic. They make money regardless, but I think this is probably one of their smartest decisions.
But they are thinking ahead. This is step one. If this is successful we could have a third movie, we have new toys, new merchandise, and many more things that even we might not know.