<Staff edit>
I can see how you get there, but I think that's something of a miss.
Given the very clear demographic distributions of religions, down to some very localised variations which can be traced to historical migrations of people (rather than the relevant ideas, on their own) religion gets a massive input and influence from human culture and, despite numerous individual exceptions, this is essentially determined either by the dominant beliefs in local society or by one's immediate family if different from the local majority.
It's not gullibility that produces this effect or a breaking of it but rather the propensity to doubt and question, and the willingness to think about breaking away from the social or family mainstream orthodoxy.
Some societies raise children such that the idea of doubt and questioning is itself difficult to conceive of. Others are somewhat more open to teaching about sceptical thought and the value of a questioning mind.
The gullible however, I suggest, will be largely locked into whatever religion or world view they were raised in.
Having taken one such on board, most often without question, this "first in" will almost always have tendencies to shut the door on any other questioning or consideration of alternate understandings and perspectives.
Shutting the stable door because the stable is now occupied.
Perhaps the people to look for are the ones who have already had to make major changes of mind at least once, due to questioning or due to forced exposure to new information and ideas
We are told that is what it took for Buddha: a new exposure to examples of sickness, crippling old age, and death, breaking through both previous (arranged, comfortable) experience and teaching.
edit for P.S.
Perhaps I had it easy in some respects, here: whether or not I had a large dose of questioning in my make-up (probably I do), I certainly grew up far from naturally in-tune with the thinking of my family or of my local society.
Turns out there were good reasons for me being an "outsider" despite my best attempts not to be.
Late discovered, but that's autism for you.