Uhm, because I'm not a moron, that's what. I know that the religious convictions of the US military closely mirrors that of the US population (although most studies show the military ranks are slightly less religious than the US population at large), and that there are plenty of atheists in and out of the military. I also know that the "atheists in foxholes" phrase most often used to express
the belief of the speaker that all people seek a divine power, or anything else to get them out of the situation they're in, when they are facing an extreme threat, such as when under fire in war time or in Chicago, or on trial in court, or when confronted by two or more former girlfriends at the same time. I'm sure there have been many instant (if only temporary) conversions to a belief in God during a time of extreme threat, just as I'm sure the very same situations have caused many to question their own existing belief in God due to the death and violence around them. Plus, there's the
Military Association of Atheists & Freethinkers - Atheists in Foxholes, in Cockpits, and on Ships (with some very interesting comments by some highly decorated soldiers very experienced in combat - all of which will be ignored or dismissed by those who think there really and truly are no atheists in foxholes).
All it takes is one atheist who has been in a foxhole to prove it one way or the other, and we have many first-hand accounts of those. It's such a silly, albeit humorous aphorism, that proof shouldn't even need to be requested, much less given.
So the fact that you don't recall hearing anyone
not praying is supposed to mean something? Relaying such a classic example of direct personal experience anecdotal evidence is an example of many logical fallacies, most notably the informal fallacy combined with the Conformation Bias logical fallacy (also known as Confirmatory Bias and the MySide Bias) where people tend to collect, remember and favor information that confirms their beliefs or hypotheses, and will ignore or discount information which is in conflict with their beliefs. The effect is stronger for emotionally charged issues and for deeply entrenched beliefs. For example, in reading about gun control, people usually prefer sources that affirm their existing attitudes. When talking about religious issues, they prefer only those sources which side with their own beliefs, and will dismiss any evidence, empirical or not, which is in conflict with those beliefs. In this case the information you recall is already biased to begin with, and you've chosen to draw conclusions based on that bias. Because of the incredibly small sample size and personal bias of your anecdotal evidence, it can only be considered at best a dubious support of your claim, regardless of the veracity of the claim. it could very well be that every single firefighter on the fire line was religious, or an instant convert, who not only prayed, but prayed aloud and loudly instead of silently, but it doesn't really prove anything for which any kind of valid conclusions can be drawn, especially in light of the contrary evidence of larger sample sizes.
Since you were not there, you did not observe them. Therefore, since you did not see, or hear, them yourself, you cannot prove them to your self, therefore, in your mind, they may not exist but you may reluctantly agree that it MAY have happened and will hold final judgement until such time that you can see or hear it yourself. That is all because you don't wish to believe in ANYTHING that you cannot see, hear, taste, touch, smell etc yourself. 
