Maybe not more efficient, but maybe more resilient to electromagnetic storms, not prone to overheating (maybe), etc... Maybe it's about fitting constrained scenarios.
It seems like they may be prone to overheating in some fashion. All that electricity and motion has to cause some kind of thermal load. Or am I way off base?
Yes. Friction is usually the limiting factor in mechanical systems. It causes a lot of heat, noise, stress, and wear on all interacting parts. It requires all sorts of messy approaches to mitigate, such as lubricants and bearings. Electricity is basically magic by comparison.
