Ahhhh yes the famous cash faucet that just needs to be turned on. Why would anyone that could have been making more money not made it before? Growth and profit are not mutually exclusive.
MySpace did what you suggest. They monetized heavily, harming UX, and creating space for a cleaner modern user-friendly competitor. That's part of why they failed.
I think they're just waiting until they've completely solidified their #1 position to concentrate on making more money. It will seem obvious in hindsight that they make $20+ billion, the way it does for Google now. It may never be quite as good as Google though, but max potential is especially hard to predict.
But if you are constrained by your team (ie, you can't work on everything at once, which Facebook says is their biggest constraint) and you have plenty of easy money from investors, why would you try and profit now and risk another service taking your audience when you could possibly build something that can profit for years to come?
Constrained by your team? I can see you making that case for Instagram with only 12 people, but according to Yahoo Finance, FB has about 3500 people. Not one of them is thinking about how to increase revenues? And they don't have enough engineers to try out some of the ideas?
I think they're just waiting until they've completely solidified their #1 position to concentrate on making more money. It will seem obvious in hindsight that they make $20+ billion, the way it does for Google now. It may never be quite as good as Google though, but max potential is especially hard to predict.