As others have said, moving hull material beyond the engine mounting position provides added transom lift which allows for better boat control when operating from a tiller which is usually a problem as the bow is usually up in the air and you have to get on a good plane to get it down so that you can see and control your boat better. This way you have better control at slow speeds too, which (opinion BTDT) is where you spend most of your time anyway.
On the Texas coast, growing up, that's where "live bait" boxes were mounted, ensuring that they would be in the deepest point on the boat to ensure fresh water was always available for your bait shrimp.