Why is it logging "Reference Error" in the first case, why didn't it pick it from the global scope like in the second case?

Question

Why is it logging "Reference Error" in the first case, why didn't it pick it from the global scope like in the second case?

let a = 10;

function test1() {
  console.log(a);
  let a = 100;
}

test1(); // Reference Error

let a = 10;

function test2() {
  console.log(a);
}

test2(); //10