"Isn't there a reason why single women that age etc. are single too, then?"
Well it's usually because their husbands/partners have left them for a younger model.
Or they're single because they want to be or there is a reason and they have a "flaw" that makes them unsuitable relationship material.
But I reckon there are more single, eligible older women than older men. Precisely because there are more men with younger women than the other way around.