Since humans developed cognition [millions of years ago] the first thing they are aware is humans die within a certain age and no one is immortal.
In general the majority do not have a conscious fear of death because it has been suppressed.
But if you analysed your own internal self, the root cause is the existential crisis [a mater of fact] hidden within yourself that drive you to cling to theism as a psychological comforter.
If you don't have a qualification or training in psychology which enables you to practice as a psychologist, attempts at psychoanalysis are speculative and are likely to be labelled as pseudo psychology – you can't really object to that description if you don't have any qualifications in that field. You are attempting the extremely broad psychoanalysis of all
human beings dating back to our origins, and claiming that you've isolated the cause of all
religious beliefs, which is of course highly speculative. As has been explained to you, existential crisis can be related / attributed to many human behaviours, but in saying that, as I'm not a psychologist and don't have a qualification in psychology, it is a speculative statement, not a certain reflection of the truth. So I think it is an error of judgement or logic on your part, to claim that you've established your claims re existential crisis as a matter of fact.
There could be any number of factors working together which cause someone to be a theist, your isolation of existential crisis as a root cause is something which can be falsified simply by a theist disagreeing with that conclusion and explaining a different “root cause” than you postulate, how could you prove the theist wrong? If you are going to insist that existential crisis is the root cause of theism despite theist's claims to the contrary based upon your ideas, you are only confirming your ideas and beliefs to yourself without having any evidence which supports that claim, not necessarily making a substantive claim about reality. I think that with any claim that cannot be verified or that is based upon our inferences, we have to accept the strong possibility that we could be wrong, but you've gone to the opposite end of the spectrum and are claiming that your ideas are a “matter of fact”. In this case, perhaps your overlap of psychology with philosophy is too extreme.
In many cases you refer to statistical evidence as a reference for supporting your claims. If statistical evidence showed that existential crisis was not a huge factor in why people are theists (note, that I believe it is a / one factor), would you acknowledge that evidence as an accurate reflection of theism or persist with your claim that existential crisis was the root cause of theism as a matter of fact?
Once a theist, now agnostic.