It comes together quickly, though. They don't need to learn how to become a company that knows how to sell advertising; they can instead just pay some other entity to do that.

It's OK to not have complete vertical integration. (They probably don't fix their own toilets, either.)

And if it makes as much money as it seems must be possible, then they can just buy one of the advertising partners that are already have plugged into their system and shitcan the rest.