I had a conversation with another semi-famous PL designer. Not one of the ones you list, but only a little below them. He primarily worked on languages the C/C++ family, and had no conception of the value of a closure.

There are lots of smart PL designers working systems languages, and there are lots of smart PL designers working on high-level, functional languages. That doesn't mean that either group is necessarily aware of everything the other group is doing, and it doesn't mean they share the same goals, experience, or taste.