quote:

As with many things, the origin of this convention is historical. Briefly, the reason why a DI box is necessary to connect an electric or bass guitar directly to the mixing console is that the pickups are strong in voltage but very weak in current. The microphone input of a mixing console requires a good helping of current; the line input doesn't need so much current, but still more than the pickups can supply.

However, the mic input requires only a small voltage. So if some of the relatively high voltage from the pickups could be exchanged for current, then it would drive a mic input perfectly well.