According to Spengler (a columnist for Asia Times):
Why do Muslim apostates gravitate towards atheism? That is not true of other religions. Many Jewish converts achieved prominence in 20th-century Christianity - for example, the recently deceased Cardinal Jean-Marie Lustiger, the martyred Carmelite nun Edith Stein (now canonized), and the great Protestant theologian Eugene Rosenstock-Huessy. But the name of no prominent Muslim convert to Christianity (much less to Judaism) comes to mind.In the real world, Jewish converts to Christianity (for example, Saint Edith Stein) almost always go through an atheist or agnostic period first.
Maybe converts who start from Religion X are more likely to go to a religion that regards Religion X as dated. Christians frequently classify Judaism as something out of date but think of Islam as off that timeline entirely. Atheists, on the other hand, think of all religions as dated.
If the above theory is correct, atheists who become religious are more likely to start from the New Age brands of secularism (instead of the materialist brands) since those can be plausibly classified as pagan and most religions think of paganism as dated.