I've always said that I don't think that BB understand the value of pronouncable 4/5 letter domains. I wouldn't list any 4 letter domains with them simply because I feel they are undervalued and the amount of pronouncable 5 letter domains of mine they've rejected, to me is shocking.
Dorans stats show that by percentage, the greatest sales are 4 letter domains, followed by 5 letter etc. If you go to the likes of namestation, everyone wants a 4/5 letter domain.
I honestly think this is BBs only weakness, they could wipe out sites like Catchy.com and own the marketplace if they listed every pronouncable 4/5 letter domain submitted to them. Not only that, but their users are not going to drop these domains... which can't be said for many of the domains they are accepting right now.