Good point, but I think the reason why FB and YT are failing to make decent profits is because they choose to. Each are trying to monetize a model in a 'certain' way and not considering drastic measures that would make each very profitable. Imagine if YT started charging for accounts. Sure their numbers would drop dramatically but the remaining, paying accounts would mean huge revenue numbers for YT and would cut their server costs by a huge %.
Is it ironic that a social network for dogs knows how to turn a profit–but not a certain social network for humans?