It is a legitimate question, I think, to ask why God made Men with such a strong predisposition to selfishness?
The usual Christian response - to point at The Fall of Adam and Eve, and the propagation of Original Sin - does not suffice, by my understanding. Since this merely kicks the can back to the question of why God made A&E the way He did; and made the world such that they fell; and that this sin was then transmitted to all Mankind.
I came across a neat explanation in a recorded talk given by William Arkle in (I think) the early 1990s (which is not publicly available).
The basic framework is that God embarked upon creation with the intent of enabling Men to become full Sons and Daughters: that is, grown-up divine friends who would become participators in the work of creation; or co-creators working within-God's primary creation.
For this to be worth doing, each Man needs to bring something unique to himself to the work of creation - something that God does not have and could not contribute.
This is what happens by our mortal life followed by death and our resurrected life in Heaven - should we choose to accept this gift from Jesus Christ (willingly embracing the necessary conditions)
Therefore (by Arkle's account, modified somewhat by me):
God chose to create Men with a strong sense of self - even to the point of being naturally selfish (such as most young children ) - and in a world (i.e. this mortal life) that would often sustain that strong sense of self.
God's hope was that some men at least (all ideally, but in practice only some) would arrive at a point of totally isolation of the self, total self-ish-ness of perspective; without any compelled belief in God and with no perceived obligation to the divine plan...
Then - wholly voluntarily and from positive and loving motives - would make the choice to join-with God in his work of divine creation.
So, innate selfishness was a necessary baseline for Men; but God's hope was that those Men capable of love would come to realize the futility of this selfishness; and would willingly accept Jesus's gift of resurrection into an eternal, wholly-loving and creative life in which our self is voluntarily fully-aligned-with God's creative motivations.
This strategy can be more clearly understood by considering the alternative that God made Men wholly unselfish, without even a distinct self, and already-immersed in God's creative motivations.
I think it can be seen that such a creature would be useless as a divine companion in the work of creation.
This alternative is indeed, pretty much, the world view of Eastern religions such as Hinduism and Buddhism - which regard the self as an intrinsic evil (or illusion) and strive to extirpate the self; and to join human-beingness wholly with the divine purpose.
For a Christian, by Arkle's account; this mortal world is a vital place of learning - without which we cannot become the both self-centred and loving-creative companions that God desires.
In complete contrast; we can see that 'Eastern religion' (pretty much) regards this world as an illusion that must be overcome for us to lose the false sense of self, and re-assimilate with the divine purposes.
Anyway - the main point I intend to convey here; is that this is an explanation of why Men are made the way they (nearly-always) are, and this mortal earthly life the way it is; and to show how this makes sense and is indeed necessary -- given the assumptions I hold regarding what God is intending by creation, and what Jesus made possible by Heaven.