Why is "use strict" prohibited in functions with non-simple parameters?

I have questions
1

What's the rationale for making this code a syntax error?

function foo(a = 1) {
  "use strict";
  console.log(a);
}
2

This reddit thread points to tc39-notes/july-29.md at 4c6534b52ca829f74ed75e4fe78b74f5a55dc0bf · rwaldron/tc39-notes · GitHub

3

I see, thanks!

I wasn't aware that the parameter list is evaluated with the strictness of the body. But considering that

function foo(x, x) {
  "use strict";
}

Is an error, I can see the motivation.