Because our TEs aren't wearing numbers in the 40s anymore? So they take more of the 80s range?
And if you look around the league, you'll see a similar trend. The Cards, Chiefs, Falcons, Panthers, and Texans don't have any receivers who wear 80s numbers.
Less than half the league's teams have 2+ WRs who wear numbers in the 80s.
The only teams with 3: NYJ, CLE, TEN, NYG, TB
The only team with 4: GB