The second reason is that excellent people are busy making friends with better people. They are surrounded by interesting souls, and they lead interesting lives themselves, so they are also very interesting. There is no need to find someone to get rid of being single for some other reason, so most of them are single.
The third reason is that excellent people generally have high standards for choosing a spouse. They often like people who are as good as themselves and can make progress together, but there are not many such opportunities, so many people are single.