It only assumes that single characters are desirable variable names. Especially if (as in Lisp) one does not draw a conceptual distinction between variables and functions, it is common to see multi-letter variable names.
Here is a typical example of a modern research paper:
Most variables are one letter, but notice, e.g., GL in the fifth line (the General Linear group, not G times L), ker in the seventh, etc.
One reason for brevity is that we like to write on paper and/or the chalkboard.
And to answer your last question, I think math does concern itself with readability. Many mathematicians are obsessive about making sure that their work is as readable as possible, although unfortunately this is not universal.
Comments
It only assumes that single characters are desirable variable names. Especially if (as in Lisp) one does not draw a conceptual distinction between variables and functions, it is common to see multi-letter variable names.
Here is a typical example of a modern research paper:
http://math.stanford.edu/~conrad/papers/locchar.pdf
Most variables are one letter, but notice, e.g., GL in the fifth line (the General Linear group, not G times L), ker in the seventh, etc.
One reason for brevity is that we like to write on paper and/or the chalkboard.
And to answer your last question, I think math does concern itself with readability. Many mathematicians are obsessive about making sure that their work is as readable as possible, although unfortunately this is not universal.