Hi,
because all the transmitters will be driving the line all the time!
not fully correct: using a time-triggered communication makes it is possible. Do not think that I am so clever (=
The idea comes to me from work with CAN. First of all, each slave device must have open-drain output. Now, the master of a net sends a marker or other specified data packet (request). When slaves catch it then they start a wait delay. Each slave has own delay time depends on its number, priority etc. After delay is done, slave comes to active state inside own time slot in which it may send return message if needs. By this way only one device can send a message at time; all other are passive at this time.
Good days!