Scribes were very rare in the Mesopotamian society simply because there weren't many educated people, and that is why this profession was highly respected. Bureaucrats also were a minority in the society and because they were bringing the important decisions, it was important for them to be literate.
Shepherd were illiterate and uneducated, but this didn't affect their profession, as they didn't needed it. Priests existed even before the cuneiform was created. Blacksmith had a similar position as shepherds in a sense that were not literate and were not obliged to be.
