The general thinking with the bigger straight programs is that a surfers surfs in a certain comfort zone/circle.
E.g. TGP's have a large % of bookmarks.
Bookmarks simply mean that surfers come back day after day.
Those same surfers have seen Site X being offered about 10* so part of the shelflife is being driven by webmaster demand.
Having a site that generates e.g. 100 sales a day will drop then to 70 but the new site will pick up 90-100 .. thus a positive balance.
With guys like this it's a simple logistic and numbers game.

This is only for the real big programs. Sites with just 8 scenes should be banned. Barriers of entry in this market are way too low.
Visa approves a site these day. I've never seen a complaint on content levels which is insane.
Minimum quantity of content should be at least 32 days at max download speed.
My 2 cnts.