How so?
Because it is.
That's common knowledge. Children are born without knowing a lot of concepts. We learn about abstract concepts in elementary school (if that-I haven't been in awhile ). You ask a toddler or so have you that haven't heard of the term god and think he will give an answer "creator" would be far pressing it. Also, think of children who haven't been born and raised in a christian dominates environment. I was told by one male from china who didn't identify as an atheist (didn't care about it) said in China there really isn't a profound set religion that people just grow up without knowing any religious concept altogether. Plus, belief in a creator has so complicated even Hindu vs. Christianity-how on earth would a toddler or elementary school kid would know that.
They're introduced to theism when they are young. They weren't born into believing in god (a lot of the population don't even believe in the christian god), they were taught god. Take people who were born and raised Buddhist, Hindu, so have you. How would they have any concept of a "creator" defined and determined by abrahamic traditions.
It's not really a theological thing, but just nature and nurture.
It's not "common knowledge."
Can you explain the differences in dispositions of identical twins born and raised under the same conditions?