Why does the position of where you add to a return value of a recursive function matter?

I’m trying to figure out why the following returns 10 correctly:

    function recurSum(n) {
      if (n <= 1)
        return n;
      return n + recurSum(n - 1);
    }
    console.log(recurSum(4)) //output 10

but when you add “n” after the recursive call in the return, you get the wrong result. The following returns 6 incorrectly

    function recurSum(n) {
      if (n <= 1)
        return n;
      return recurSum(n - 1) + n;
    }
    console.log(recurSum(4)) //output 6

Why does this happen?