Two CAN buses is a quite low number. Last system i saw, which was pretty old, had at least half a dozen from what i could tell from my end of the system, probably even more internally inside or behind other components. Modern cars also use flexray, LIN, MOST and all other kinds of buses. The reason for this is safety, bandwidth and that the delay jitter on a highly loaded can bus can be relatively unpredictable for high frequency control requirements like suspension, traction and other engine related control.