The outer CV joints in cars are Rzeppa joints. The inners are not.
As you can see from page 2 of the attached drawing
http://tijil.org/Scion_Docs/05_tC_Shop_Manuals/Repair%20Info/Repair%20Manual/Drive%20Shaft-Propeller%20Shaft/Front%20Drive%20Shaft/conponen.pdf
the inside CV joints are of a different design.
Rzeppa joints transmit constant torque while allowing varyng angles, but the axle assembly as a whole has an additional need… If you follow the movement of the wheel hub throughout its suspension travel, you’ll find its distance from the transmission changes as the A-frames control the camber via their respective arcs (or the struts if they’re used). That requires the axle assembly to be able to change length as it transmits torque. The design of the inner joint allows
- constant torque to be transmitted through the axle
- the inner axle to change angles to accomodate suspension movement
- the length of the axle assembly as a whole to change length to acccomodate free movement of the wheel through its geometries.
EDIT: Rod, you beat me. I MUST learn to be more succinct!