two reasons. first reason is that doing DMSA on the cutler protocol requires you to wake up in the middle of the night to dose. cant do it. totally screws up my sleep. just does not work for me.
secondly, after reading many many testimonies it seemed to me that people generally had better results with DMPS. more people reported nearly miraculous results with DMPS than with DMSA. not all of them, but it weighted in favor of DMPS. it seemed like DMPS worked faster and more completely. but thats just my impression from reading other people's testimonies.