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?
You can include what you deem unfit in the Natural Selection process too. Humans are part of reality, part of nature, part of Natural Selection process/environment.
A crop that can only survive with human culturing may be unfit without human intervention, but humans are there culturing it. The crop survives. The crop even replaces other crops that humans may have cultivated otherwise. The crop is still being naturally selected. So you have to include humans and that process in Natural Selection.