The download-link trickery was probably relatively ineffective, since most people only needed one download to figure out how it worked. There were a lot of people who paid for premium Megaupload accounts so they could download stuff faster and without limits. It was like the Amazon Prime of bootlegged content in some circles.
There are billions of impressions being sold daily for advertising from hijacked users. Big $$$.
Advertising revenue was secondary to premium memberships, but now paypal, visa/mc are shutting down file lockers payment processing and they are more reliant on ad revenue.
