Well the whole aos and dos stuff was probably beacuse the same thing that happened during sotn happened again in 1999. That being, there was a huge shift of power.
Except this time he didn't go to sleep, maybe cause of the whole soma deal. He had to make sure his father's soul is gone forever before returning to his sleep, but then Soma was born.
So technically it forced him to remain around, since unlike sotn where everything returned to normal once he beat some sense into Richter the 1999 event could've left something behind, a lingering feeling that it's not over yet.
It's still a better reason than Alucard going against his beliefs because he just wanted some action.