`𝜋` is a mathematical symbol, but you could also write `CircumferenceOfCircleWithUnitDiameter`. The reason everyone prefers `𝜋` should be clear. The same is true for a less extreme case like `fst` and `first`: You don't need to think about what `fst` means, if you are fluent in the programming language it is clear, and more concise than `first`. `fst` becomes an atomic symbol in the programmer's mind, it is not something you need to interpret like `first`. This is not about communicating with other humans or even the computer, it is about efficient representation within your own mind.