The terms allow you to be very precise with what you mean when talking about them. Knowledge of what a functor is transcends any particular codebase, meaning we could all name them mappable or whatever made sense to us, but then every code base would have a different name for the same thing and it would be less clear.

A shared precise terminology helps everyone get on the same page faster. It’s the same as when you first heard that text in computer programmes was called a “string”. Strange word, but once you know it, it’s fine.