I'm a bit curious about your assertion of "should" about A/G providing ATZ traffic information?
At a busy airfield with no radar, it can be very difficult to keep track of all the traffic in the ATZ. Remember, it remains the pilot's responsibility to see and avoid other traffic, and you can't assume that a FIS or A/G service will give you the complete picture. Neither can you assume, of course, that another pilot hasn't done something stupid without notifying the radio service.