It's probably something decided by state education boards, so whichever map your state decided was all you saw for twelve years. Leading you to think the entire US had the same.
Although it can seem pettily nationalistic (and probably is to some extent), for quickly illustrating "You Are Here", and the relative positions of other countries to your own, centring maybe makes more sense than having some far away country at the centre.
It seems pretty common/natural in different countries too. I wondered if a 'most accurate map' exists, and found Authagraph:
https://ourplnt.com/wp-content/uploads/2017/06/AuthaGraph-wo...
https://ourplnt.com/authagraph-probably-the-most-accurate-wo...
It's not difficult to find the origin country of the map, Japan.
As an aside, I also had 6 years of American Revolution, all told. Every time we moved, the new district would be starting that unit. So annoying