"most common" does not mean "everyone".

If there are 100 people and 2 are truck drivers, but the other 98 all have different jobs, then truck driver is most common, but there's still not a lot of truck drivers.

Most Americans are retail salespeople, followed by cashiers, and then cooks.

http://www.bls.gov/news.release/pdf/ocwage.pdf

Guessing you've never been on a US mainland highway.

HONK! HONK!