At present science explains moral responsibility based on the natural evolution of humanity and the necessity of a cooperative social structure independent of the necessity of moral responsibility, It still remains that the development of Compatibilism is based on the philosophical/theological necessity to justify some sort of freedom of choice based on moral responsibility. Also the dominant reason for the believe in Libertarian Free Will is a theological justification.I do believe that the debate over free will has its origins in the theological debate over whether an omniscient, omnipotent deity is justified in blaming its creations for disobedience to its moral commands. That is an ancient debate that is very much alive for those in our current era who still take the old creation myths seriously. I do not. Nevertheless, that does make theological debates over free will relevant to the secular debate that more modern philosophers have taken up over determinism and free will.
Compatibilism (Stanford Encyclopedia of Philosophy)
plato.stanford.edu
Compatibilism is the thesis that free will is compatible with determinism. Because free will is typically taken to be a necessary condition of moral responsibility, compatibilism is sometimes expressed as a thesis about the compatibility between moral responsibility and determinism.
Yes some atheists and non-believers justify some form of Compatibilism for the need of moral responsibility the need to justify moral responsibility is based in older philosophical/theological requirement of moral responsibility.