AWK: why does $(cat) work for stdin, but $* doesn't?

echo '((3+(2^3)) * 34^2 / 9)-75.89' | awk "BEGIN{ print $(cat) }"

The above syntax works fine with the calculated result '1337'.

echo '((3+(2^3)) * 34^2 / 9)-75.89' | awk "BEGIN{ print $* }"

But the above syntax doesn't work, though there's no error.

Plz advise.