Consider this scenario. I am merging right to make a right turn.
- Indicate right
- Wait for a car to give way
- Merge one lane to the right
This doesn't work with automatic cars because they don't understand hand signals. Instead I just have to merge and hope the overtaking cars are going to give way. If this behaviour becomes common, people will start merging without indicating in the expectation that automatic systems will take care of the resulting conflict.