[throwaway192874]

There's a book called "Zero: The Biography of a Dangerous Idea" that goes into the history of zero in detail, admittedly I haven't finished reading the book myself but got at least partway through and it was fascinating to read about it and I'll one day finish it :)

What you said about it not being in the numeric system is definitely part of it (ex: roman numerals not having it) but also all the problems that come up with zero have to be dealt with (e.g allowing dividing by it allows you to prove anything, and there's a great proof that winston churchill is a carrot in the book showing as such), and there's some overlap with religions in fearing "nothing" and what that might mean