Why do Atheists borrow suppositions from Theists when they want to pretend they are intelligent?

I see that some parrot like 'genuises' of Atheism, use Rene Descartes famous maxim "I think therefore I Am". Rene Descartes was a Theist, not an Atheist. Therefore, 'Why not use Atheist philosophers maxims? Is it because there are so few Atheist Philosophers? Or is it because Atheist philosophers are not intelligent enough to invent suppositions?