It's a popularity contest.
All-Pro = best at your position. Lewis did tie for 2nd Team AP All-Pro one year, though - that does mean something. Still, there just weren't very many good tight ends in the league in the early 2000's - not at all close compared to today. So you are wrong about their not being close based on Lewis' comparison to his contemporaries and Pitta's comparison to his. Lewis' prime was a bad era for tight ends.