Adding `null` to C was very simple to add. It added a lot of complexity that the language designer did not see coming (hence the billion dollar mistake he made on that).
`NULL` was originally added to ALGOL back in 1965. C was not even a thing back then. It was obviously a bad choice to port NULL to C, one that ADTs would have perfectly modeled, without the billion dollar cost.
In fact C was built sometime around the early 70s, and at the same time the first MLs where also being developed. One added null, while the other added a better mechanism for "nothingness".
Bottom line is you cant compare "adding null" and adding a feature that is over 50 years old, one that is battle-tested thru generations, and still holds up.
