I design a lot of CLIs, and I wonder this, too. I think it's two things. First, it's very hard to attach meaning to a single character. Many early Unix tools we

I design a lot of CLIs, and I wonder this, too. I think it's two things. First, it's very hard to attach meaning to a single character. Many early Unix tools were two-character, which is just enough to remember and to be unique. Second, many (not all!) Unix people have been reluctant to pollute global namespaces. Anyone building a CLI tool for the use of others knows that it's going into a complex environment with many other tools. If it become commonplace to create single-letter tools than there would be constant conflict in that namespace. In my experience, groups of geeks are often aware of the tragedy of the commons, and able to act in concert against it.