Why did nasus get a buff exactly?????

I honestly don't understand riots thinking in buffing unnecessary champions, nasus was insanely strong as it was before with his q stacks getting insanely high and then just pressing w to make his target 200 movement speed and when it ends he can just use it again. But now whenever he ults he gains 50% cooldown reduction on his q???????? I really don't understand why he has gotten this it just feels like he is unstoppable 10 minutes into the game where he just continues to stack while he 3 shots whatever top laner he is against. If they do this big of a buff to nasus why hasn't other champs that are forgotten like aatrox have some sort of buff this big.