The reason why rm and mv are are first class citizens is because they correspond to libc/system calls (unlink and rename). "cp" has no libc/system call equivalent.

commit 76dc18c99a3b30f91d5f3a7007b972081af9bc09 Author: Martin Nilsson nilsson@fastmail.com Date: Fri Feb 9 19:24:29 2018 +0100

Put cp() in the global scope, as rm() and mv() are already there.

So polluting the global namespace with cp is not necessarily a logical step.