There are many prosecutions brought for careless and dangerous driving when no injuries have occurred. The problem in the situation you describe is that to succeed with a prosecution there has to be evidence that the driving exhibited by one or more of the participants has fallen �below that expected of a careful and competent driver� (for careless driving) or �well below that of a careful and competent driver� (for dangerous driving).
The fact that an incident has occurred does not necessarily mean that this can be proved. It nearly always requires witnesses to provide statements and perhaps to give evidence in court. Most witnesses simply want to resume their journey without further ado. They are usually not prepared to �become involved� in something which is very often in an area far from their home. The police know this and do not trouble to seek out evidence in all but the most serious cases - usually those involving death or serious injury.
If all drivers drove carefully and competently all of the time there would be far fewer collisions. Very often incidents that are described as �accidents� are nothing of the sort and are the result of someone�s bad driving. However, proving it in court is another matter and that�s why there are far fewer prosecutions than collisions.