Earlier quoted context omitted.
People who tend to be interested in philosophy and are theists probably tend to go into religion rather than philosophy.
That's one hypothesis. An alternative hypothesis would be to suggest that the more educated one becomes in philosophy the less that religion makes sense, and the clearer it becomes that there is no evidence for theism. (Note, I'm not advocating for either of these hypotheses, but correlation is not causation.)
I suppose Georg Cantor might be an exception to this.