

Evolutionarily speaking, threats from outside are an existential threat and need spreading. Good deeds at home are already known by everyone who matters and the ‘reward’ is survival of your children, not you ‘feeling good’. People do ‘hero worship’ though. I think you are downplaying that. Though the influence that comes from such a position probably means people are inclined to cooperate with ‘power’ because it has, de facto, already shown itself to be powerful. Whereas those ‘asking’ for power are necessarily weak.
This is all pop-sci evolutionary psychology so discard at will…
Simply put, because you often want to change the state of something without breaking all the references to it.
Wild off the top of my head example: you’re simulating a football game. Everything is represented by objects which hold references to other objects that are relevant. The ball object is held by player object W, player object X is in collision with and holds a reference to player object Y, player Z is forming a plan to pass to player object X (and that plan object holds a reference to player object X) and so on.
You want to be able to change the state of the ball object (its position say) without creating a new object, because that would invalidate how every other existing object relates to the ball.