Realtors will never sell a pre-sold for me, why not?

I have never sold a pre-sold through a realtor, I have offered very good money for selling a pre-sold but have yet to sell one through a realtor. I offer a very nice package at a very reasonable price and a lot of realtors know that but no one will sell one on their own. Little do they know that when things are good I would give them all of my business which is highly lucrative. Please tell me what I am missing.