Two possibilities:

They are comfortable pacing off of you.

They are using you for cop bait.

I have both done this and had it done to me. I usually crusie at just enough above the limit to get a scowl from the officer, but not enough to wake him all the way up. It's also a way to break up the tedium of a long road trip. (I do a 12-14 hour run down south once or twice a year) One fellow followed me for about four hours and when our routes finally diverged, he pulled up and waved.

A name for this breed? Dunno. Maybe we should come up with one