I read an interesting piece by a former pro about this - can't remember who or I would link - and he was saying that whilst this is one of the biggest moans of fans it is not as straightforward as it looks. He was saying that absolutely the best corner is hard, fast and misses the top of the first defender's head by a tiny margin so getting the ball six inches over the first defender was just as bad as hitting him.
He said that people who moan about hitting the first defender don't understand the tiny margins in professional football.
Sounds like a poor excuse to me