Marketable version numbers are quite useful. If somebody says they are running 10.12.3, the first thing I do is check which version I am running to see how that compares. On the other hand, if somebody says they are running iOS 12.1.2, I immediately know that is a patch of the preceding year's major version.
The reason is that Apple actually applies marketing to their iOS version numbers, but doesn't do the same for macOS, because incrementing the minor version isn't marketable. Their crack marketing team does come up with funny names for macOS releases, but few people remember the mapping between those and the actual version numbers.