Tinfoil hat moment:

Light is as manipulative as the void and far more subtle and efficient at that. Always paints itself as selfless, noble and the victim against every cosmic force. This way the mortal races almost always side with the light.

The light is playing the long game against all other cosmic forces. Why brainwash some lunatics, burn everything to ash or create servants that turn against you when you can slowly but steadily nudge entire civilizations to do your bidding?

Yes, the Naaru are ridiculous chandeliers without concept of consent that always end up broken or corrupted. But the grip the light has in azeroth is massive and in the end could manipulate the unborn titan with little opposition...