Trying to Run Away When There's No Chance

Why do people do this? I'm talking about those people who are in like a 1v1, both are low health and in auto range, and then one of them for some reason decides to turn around and try walking away, like character has no way to outpace the person, only real way to survive is to continue to fight and try to come on top, but they stop attacking and then try to walk away and die within next 3 seconds. Why do people do that? There's no point in it. I see it quite often.

The other thing that annoys me that I see people do often is when people refuse to jump in on a fight until their teammates are already dead. Like someone just farming not 10 seconds away and people are pinging him to help in a team fight and then they all die and then that person finally comes. Or when someone leaves a team fight, and then comes back after everyone is dead. Usually their death follows shortly after they try this. I don't get that mentality, like if you weren't going to join the fight when your team is up why did you join after?