To be fair though, there is a wide spectrum of "usefulness" for pure mathematics concepts in applied mathematics. For less contemporary examples you don't need to know about Lebesgue measure to do practical numerical quadrature for applications. Or you don't need to know that rotation matrices are part of the SO3 group to do computer graphics. Sometimes the abstractions are powerful and sometimes they are kind of a distraction (or even make communication a problem). There typically needs to be a super compelling application to motivate a shift in baseline knowledge.