Every cell, virus, plant, or animal mutation or characteristic is explained by Natural Selection.
It’s almost like there is some motivation for it to make sure life exists and survives. But why do anything at all? If there is a God then it makes sense that it was put in place for life to exist but if there is no God then why don’t we just have a universe of non-living matter?
It exists because we wouldn’t be here if it didn’t. That’s all there is to it really. You’re asking for an answer if “why”. Why did the earth form in the exact place that it did? Things are allowed to arise randomly, and natural selection isn’t an explanation for the begging of the universe