[GeorgeTH]

...don't forget there's a good number of Thumb TGPs who list nothing but sponsor hosted galleries, and another group who mostly list their own galleries (on different URLs to give the impression of variety).
Thumb TGPs without advertising (being banners, text links, or hosted/own galleries) are rare!

Then there are a few who are making most of their money from paid listings, hence skim less to trades.