That is the theory behind having 2 unrelated parents, to maximise genetic variation and reduce any weaknesses in the offspring.Maybe it does, just seems weird to me. I thought the idea of a flower was, so you ended up with pollen from another plant, so that your species is strengthened.
Some do, Daphnia do and there is a lizard that produces clone babies of the mother. But you are right, most species do need 2 parents.Animals don't self-pollinate because you would become genetically weaker.