2 reasons; first, motors and drive electronics are both heat producing systems. In order to combine them you have to derate the assembly to prevent damage, and second, motors are designed by mechanical engineers, motor drive circuits are designed by electronics engineers. The two disciplines and attending manufacturing processes are completely different.
Chuck, A primary reason to separate motors and drives in the past has been packaging the two together, and especially the ability of the drive to handle heat. There is significant technology involved in mounting the drive to the top of the motor, but it is still an issue as motor/drive combos go up in torque (with resulting increases in heat).
Everyone has had the experience of trying to scrape the last of the peanut butter or mayonnaise from the bottom of a glass jar without getting your hand sticky. Inventor Ron Jidmar thinks he has a solution to all of that nonsense with a flexible jar design that can be squeezed with one hand to lift contents from the bottom to the top of a jar or container, leaving the other hand free to scoop the contents out cleanly.
Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.