I think the distance of I-80 through Wyoming is long enough to generate some user fees payed by fuel taxes. Most cars do have to fill up once in 400 miles, and trucks maybe not as often, but they fill up if needed, or where it's the cheapest, and as far as I know, Wyoming is one of the cheapest.
But they could build a mainline toll plaza between Rock Springs and Rawlins, no chance of shunpikers there, because there are no other roads in this area. US 287 is a 140 mile detour, I don't think many people will do that to avoid a few dollars.