The reason was these marketplaces could get multiple of the normal sell through rate via a) seo/google; b) advertising; c) hype; d) other. That multiple was justifying paying around 35% commission.
But all of them have or are losing their shine and their sell through is normalizing making their commission questionable. The typical reasons for this are a) inventory overgrowth for the same amount of search traffic/ad traffic b) (for some) favoring insider names; c) re-inventing what a good name is and pushing it to customers creating a disenchantment with repeat buyers/serial entrepreneurs d) competition
I have completely stopped adding the names, although not removed the ones already listed, as I am more busy acquiring new names than remarketing the ones that are already listed somewhere. Afternic with 20% commission is doing far better job than BB/SH/BP with their higher ones.