Natural selection was not a conscious choice. There have been many choices in grammar that have been decided almost arbitrarily by higher authorities. Sure, many of these choices may have been based on their own experiences, but they were not necessarily the best choices. They were decided by a small group of individuals, but again, the choice was not strictly a natural selection of grammar rules. Language more often follows this pattern than grammar because people are more likely to argue over grammar than language itself, excluding etymology, of course.