Possibly due to the placement of USB on most phones - at the bottom, where a drive would stick out awkwardly. Also, MicroUSB on a lot of devices doesn't seem l

Possibly due to the placement of USB on most phones - at the bottom, where a drive would stick out awkwardly. Also, MicroUSB on a lot of devices doesn't seem like the most robust port ever - I think it would eventually wear out with more than just the nightly plug/unplug for charging.