True. Also, aluminum parts are stronger than plastics. And magnesium parts are stronger than aluminum. But we don't make everything out of magnesium.

The question is not "could it be stronger?", to which the answer is always yes until you've hit the extreme end with some kind of inconel/titanium/carbon nanotube mix, but "is it strong enough?". Also cost to manufacture, including tooling costs, is an important factor in choosing the best manufacturing method for a given part.