Cross flow units have the advantage of having the radiator cap on the low pressure end of tubes so that a high volume water pump that builds additional pressure in the block (which is a good thing as it raises the boiling point in the block thus minimizing localized steam points) will not blow the seal on the radiator cap.

Further wide rectangular aluminum tubes provide better heat transfer because more surface area is exposed to the air flow as opposed to the oval tubes that must be used in copper/brass units in order to maintain strength. In these units the air flow tends to skip across the high points of the tubes instead of following the contour.

And, the obvious, the wider tubes don't plug up with precipitates/sludge as easily as do the small tubes and the radiator weighs less as a bonus.