And not to mention that assault rarely leads to jailtime even when it is reported. Jail for assault tends to be limited to serious cases of aggravated assault, assault with a deadly weapon, sexual assault or repeat offenders.
That one time you got drunk and hit somebody and they laid a charge ? The prosecutor will probably offer you a plea-bargain which avoids jail time in exchange for an admission of guilt and a hundred hours of anger management classes.
I know - I was the person who laid the charge against the drunken puncher once. I know what happened to the case.

Just because a crime CAN lead to jailtime doesn't mean it inevitably will - nor that it should. Part of what we train judges to do is to determine a punishment commensurate with the crime, considering the unique circumstances of each case.