constexpr - why just a return statement?

A constexpr function must just consist of a return statement and every argument should be known at compile time:

// constexpr functions use recursion rather than iteration
constexpr int factorial(int n)
{
    return n <= 1 ? 1 : (n * factorial(n-1));
}

Why just the return statement? I mean, why this is wrong?

// constexpr functions use recursion rather than iteration
constexpr int factorial(int n)
{
    int a = 222; //another variable
    return n <= 1 ? 1 : (n * factorial(n-1));
}