Most of the avionics packages in those airplanes are somewhat old and cannot be directly attached to a thumb drive. Even in the newer glass-panel aircraft, the entire system has to be physically removed. The primary driver for this is security and stability - you really don't want to have something that hasn't been tested and re-tested guiding an airplane on a long (or even short) flight in questionable weather.

Experience: Software Engineer, LSRM, Experimental Aircraft Builder (helped with my own avionics packages)