If they started out doing this, why wouldn't they continue to do this in the form of click fraud for advertising? Surely if they could create some minimum % of click fraud for each ad, they make more money and it would fly under the radar of their customers looking into it...
People buying ads are their real customers, users are there to be exploited.
They catch enough fraud that their customers get a positive ROI, but surely they don’t catch all of it.
They don't need to do the click fraud themselves they only need to not catch all of it. That's much less work.