In a real sense, pantheists are atheists. They believe that God (just the non-contingent ground for contingent being) is manifested as the universe—as opposed to other theistic, non-dualists who believe that the universe is an emanation of God.

However, what you seem to want to use the term (atheism) to exclusively describe is a metaphysical materialism. This is like Pantheism but without God, so of course such persons don't pray, as they happen to believe beyond all reason and logic that somehow the universe exists on its own and it's dumb but it also then produces consciousness.

People believe in that form of atheism for the same reason they believe in a flat earth or that the earth is at the center of the universe: It's certainly how the world appears to exist, and they're not going to stop believing until they're physically shown it actually exists otherwise.