American door Handles are usually round for several reasons, including:

Ergonomics: The round handle is generally easier to grip and turn, making it suitable for people of all ages and skill levels. It can be operated with just a slight turn of the wrist.

Aesthetics: Round handles have a classic and timeless look that complements a variety of architectural styles. They can harmonize with both modern and traditional designs.

Simple Manufacturing Process: Round handles are easier to manufacture and install than handles with more complex shapes. This reduces production costs and makes replacement easier.

Space utilization: Round handles can save more space, especially in narrow areas, because they do not require as much space as some lever handles.

Safety: Many round door handles can be designed with secure and reliable locking mechanisms, making them a popular choice for exterior doors.

Versatility: Round handles can be used on various types of doors, including interior and exterior doors, making them a versatile option for homeowners and builders.

While round handles are common, there are many other styles to choose from, and personal preferences and specific functional needs may vary.