Why are there so many Johnsons in the phone book?

Because they all have phones. That "name popularity search" says that five of the 20 most common surnames in the U.S. end in "son." If I were guessing the most common surnames, it would never have occurred to me to include Wilson (No. 8).

One of these days, even the Johnsons won't care if they're in the phone book. Even though all the members of the household will have their own individual phones. You know those Johnsons. They all have phones.