Black Hills "Boycott"

A reader sends this in:

My family and I recently went on a 4-day vacation to the Black Hills.  My
boys decided to play the "license plate" game and over the course of the
trip we came up with 45 (including Alaska).

Now, what boycott was that again?

P.S.  The 5 missing states were Vermont, New Hampshire, West Virginia,
Alabama and Mississippi.

Kevin Woster was wondering the same thing.