Big O notation predates Computational Complexity. It was originally used to guesstimate asymptotic behavior (limits as they approach infinity). The related Little o notation (even more specifically limits of already large values as they approach infinity) is directly related to early attempts at defining differentiation and differentiability and still sometimes show up in Calculus next to derivatives to explain how derivatives work.

The visual interpretation/intuition of Big O notation can be a useful way to build a visual intuition of what a function's derivative and integral "shapes" may look like, so some Calculus books teach Big O notation, too.