Machining is fine, but in the context of the article the problem is that it usually starts off from plates or otherwise block-shaped materials. That means that if you have a weirdly shaped part full of holes and/or with many protrusions in weird angles (as vehicle parts tend to have), then you either have to combine many smaller parts into a final part or have to machine away a huge amount of material from a solid block to come to the final shape. It would be much better to cast or forge the part into roughly the right shape straight away, so you'd need only minimal finishing work. That is what these presses enabled.