Nushell missed the one feature that every Unix shell has: if it doesn't recognize the first word as a built-in command, look it up and run it as an executable. It's crucial, and nushell is missing out on an ecosystem of random shell commands to complement it as a result. This, of course, is what makes the Unix shell so great: the many little programs able to work together via pipelines.

This makes nushell an interpreter command line, instead of a system shell.

(Yes, you can "escape" by typing ^ before a word. That's not nearly the same thing.)