A function will be called by code and go to that point in code. To implement functions, you store necessary things to memory and goto the function definition. To implement that with comefrom you'd have to have a list of all the places that need to call the function as comefroms before the function definition. It'd be a mess to read. We almost never care where we are coming from. We care where we're going to. We want to say "call function foo" not "foo takes control at line x."