Because evolution claims, via "natural selection" (in deliberate contrast to God's choice) to account for the development and characteristics of all kinds of life, including humans, it claims to account for the character traits that recognize beauty, love, morality and the like. So to be a viable system, evolution must either explain how these things evolved or, alternatively, why they're just fancies in our heads, having no correspondence with objective reality.
You're begging several questions here. The first one is that beauty, love and morality are entirely consequences of the biological structure of humans. That is certainly unproven; many would argue they're cultural constructs. Morevoer, once humans started to become capable of a culture, sometime in the evolution of the primates, the culture itself affected their evolution. For example, it's entirely likely once we started singing, women started having inordinate amounts of sex with musicians (still happens). Thence developed a dynamic whereby ever more complex musical abilities were selected for. Even without human intelligence, the same sort of evolution of complex 'aesthetic' behavior is seen in songbirds.
Fidelity, kindness etc. may similarly have been selected for as being more favorable to the raising of children. Those may be universal and innate human traits. If you can find a universal moral code that goes beyond very simple ideas such as 'thou shalt not kill', 'thou shalt not steal', you've certainly found something that's escaped the anthropological community.