One of my first professional coding jobs was in 2007 when Facebook first introduced 'Facebook Apps'. I worked for a startup making a facebook app, and EVERY SINGLE app company had the same monetization strategy: Selling ads for other facebook apps.

So the lifecycle of an app would be:

1) Create your game/quiz/whatever app.

2) Pay a successful app $x per install, and get a bunch of app installs.

3) Put all sorts of scammy "get extra in game perks if you refer your friends" to try to become viral.

4) Hope to become big enough that people start finding you without having to pay for ads.

5) Sell ads to other facebook app startups to generate installs for them.

It was a completely circular economy. There was not product or income source other than the next layer of the pyramid.

It didn't last long.

Hate to break it to you, but it’s still going on, just outside the fb app api.

Aren't most ads in scummy mobile games ads for other scummy mobile games, to this very day?