They earn a certain quantity of money from the ads you click, videos you watch and the apps you install. You get just a fraction of that money, probably something less than a tenth of it. And even more important than that, most of the time there’s not even enough ads to click, videos to watch or apps to download to able to redeem your money, so it just stays there.
They nt working free for you guys. They also getting worth out of it. For every app or offer you avail from these apps like AppMoney, mCent, Ladooo they get some comission out of it and also they earn via advertisement module as well.
So, its a mutual benefit talks where a user using App Money, mCent etc earn by investing some time and also the Apps company get worth out of it.