The real goal for the big players using these services isn't actually increasing their own users and revenue. They have better ways to do that.

Rather, the goal is to lock everyone else out from even possibly doing so.

For example: AdWords isn't about reaching new audiences, it's about staking a claim on an audience in perpetuity (as long as your budget allows). This is completely apparent from the pricing model.

Google's brilliance is that via the ubiquity of their search platform, they have effectively managed to leverage a property tax on attentional real estate. If you don't pay, someone else will move in and hopefully develop the attentional property further, raising the value Google can charge you for it until you're priced out and someone else comes along to hold onto it.