The actual signal electronics have drivers (talkers are components that produce voltage) and receivers (listeners are components that sense the voltages). In NMEA 0183, drivers can't talk to drivers because we can't listen with our mouths, and there is no arbitration mechansim to coordinate transmisisons on the wire. If multiple drivers are talking on the same wire at the same time, it becomes jibberish and the listeners get confused. A bus architecture such as NMEA2000 or Ethernet adds an arbitration mechansim so multiple talkers can take their turn and be understood without confusion, and signal collisions can be resolved by retry or error detection/correction algorithms.