Saw this show on BBC a couple of weeks ago :
https://youtube.com/watch?v=C0aK2XeDu50
Here you see AEBN's marketing director talk about their tubesites (they own a couple of big ones) bandwidth costs being higher then their tubesite advertising revenue. They actualy only do it because they can feed traffic to their paysites.
Also there is one thing nobody can offer for free ever : live shows with girls going all the way. That side of the business will never be hurt by tubesites. It's also very hard to get a positive ROI by advertising on sites that have this kind of freeloader traffic. Only the very big programs keep advertising there non-stop, probably just for branding.