Revenge killings are rare because perpetrators often don't walk away and if they do you might not walk away. There areas in my country where there are vendettas spanning generations.
Moreover, other phenomenon in low legal justice areas is that if you or your family is not powerful enough, you suck it up and shut up when someone more powerful kill your relative. Or even when equal does that, unless you are connected to one of mafias. The average person when they have relative killed in drunken auto accident wont kill in revenge.
Even criminal groups more often kill for profit or to get rid or witness then pure vengeance.