Why do you let the bounty leave?

What I wonder in this game often is 2hy do people let the bounty leave? I was ambushed by a group while I was running toward the leaving bounty. The bounty left, this group stayed behind. No one fought nor did I see anyone else that the bounty at site. These two fine gentleman just sat in bushes while bounty is leaving doing nothing, not engaging in anyway. Surely this is not fun way to play the game? I have had cases where people attack me while bounty is leaving and not letting me stop the bounty or run to stop the bounty in situations where it would not make much sense. Long range engagements mostly. Please enlighten this smooth brain of mine