They're all getting paid by the mile... And those poor bastards working for JB Hunt are governed at 62 mph, they can't afford to get much slower!!!
FWIW... JB Hunt trucks have been governed at 62 mph for a very long time. When you see one, you know to get around it. Schneider (orange trucks and trailers) and Swift may also be governed at low speeds, but since they keep changing their minds, I'm not sure where they're at now.
Most other trucks you run into east of the Mississippi are governed at 65-67. Out west you don't see too many of the aforementioned trucks on the road, as many of them are sitting on the back of trains heading for California. Once you get to the coastal states, most everyone is slow again.
BTW, the other problem is split speed limits. Illinois was the first state to come up with that whacked-out idea, but they don't really enforce it any more and may have even abolished it now. Michigan and California are the worst - In both, the speed limit for cars is 70 and trucks is 55.
So, don't always blame the trucks. Sigh.