Traffic control and to prevent the "truck stop" vibe that rich white people who will spend 30 dollars on a t-shirt with a beaver from going inside.

It also means that existing mega truck stops like TA, Loves, etc aren't in as much competition with them, and the truckers aren't buying up all the affordable fuel from Bucees without going inside to buy mediocre brisket.

It's for the safety of all other traffic. Also clearly they don't need trucker traffic, they're doing just fine with their business model.