Function arguments weren't actually first-class to begin with. In Algol 60 (of which Simula started as a superset), you could pass functions as arguments to other functions, but that's it - it wasn't a proper type so you couldn't return it, shove it into a variable, have an array of functions etc. Basically, it had just enough restrictions that you would never get up in a situation where you could possibly call a function for which the corresponding activation frame (i.e. locals) could be gone. But when Simula added classes and objects, now you could suddenly capture arguments in a way that allows them to outlive the callee.