There are no atheists in foxholes, they say, and I was a foxhole atheist for a long time. But after going through a midlife crisis and having many things change very quickly, it made me realize my mortality. And when you start to think about death, you start to think about what's after it. And then you start hoping there is a God.
Many of my fellow atheists consider all talk of 'spirituality' or 'mysticism' to be synonymous with mental illness, conscious fraud, or self-deception. I have argued elsewhere that this is a problem - because millions of people have had experiences for which 'spiritual' and 'mystical' seem the only terms available.
I'm not saying that atheists can't act morally or have moral knowledge. But when I ascribe virtue to an atheist, it's as a theist who sees the atheist as conforming to objective moral values. The atheist, by contrast, has no such basis for morality. And yet all moral judgments require a basis for morality, some standard of right and wrong.