Earlier quoted context omitted.
Are you suggesting Greek letters are not suitable for human comprehension.
Presumably the poster would have about as much as a problem if the author picked the first 14 letters of the English alphabet.also, it is not a given that everyone knows the green alphabet, and it is harder to correlate symbols when you don't have familiarity and know the names of them.
I assume they follow some standard of usage in context, but I don't know enough about economics to know what they're normally used to represent.