Why do you think so? Can't theists be agnostic about their faith, and claim that they really don't know if there is a god, but that they choose to live as if it is so for whatever reason?Technically even all agnostic and deists should be counted as atheist as well.
Deists are functionally equivalent to atheists. They don't tithe or vote according to Jesus, so they don't empower the church or have any unwanted effect on the lives of unbelievers like the Christians.
But if they have a god in their philosophy, however dilute, don't you consider them theists of some type?