Because it’s the winning option. All others lesson the chance for survival and perpetuation of the species.
Why is lessening the survival of the species an undesirable option? Again, the “should” factor is HUGE.
And why would we be “evolved” to have to propensity to violate it if it were something hardwired?
Gotta go - you can find “Mere Christianity” online, or at the library, or on audio if you prefer.
Lewis explains it better than I ever could.