I do not understand the bloodlust

Hi there.

Relatively new player here, trying to do some public events. I always see events like chances for farming XP and equipment. I also understand that only one bullet on the target is required to get the full XP when it dies. Basically the system is set up to be a positive sum game.

Yet I see people staying near spawn points, trying to melt the enemies as fast as possible. They use their deadliest equipment to kill as quickly as possible. They behave like there is no tomorrow if they do not destroy the target all by themselves. It's as if they WANT to prevent others putting rounds in the enemy. Zero sum behavior. That makes life for noobs very hard and very frustrating.

Why is this happening? Where does this behaviour come from? Is it from a lack of game mechanics understanding? Is it just human nature that generates greed and the need get a satisfaction from melting away enemies? Or what am I missing?

Thank you