This design choice is not only intentional but also essential for various practical and economic reasons.

Masonry materials used for foundation walls are typically more expensive than wood framing. By reducing the height of the masonry foundation walls as the house descends, builders can minimize costs. 

Wood framing is generally easier and faster to work with compared to masonry. By keeping the masonry foundation height to a necessary minimum and using wood framing for the upper portions, construction time and labor costs are further reduced.