Delaware is in large part a drive through state as people go from NYC/Philadelphia/New England to DC. So the roads there tend to be used more by out of staters. Look at the person I'm responding to. That makes it easier for other senators to want to contribute cash. Plus, Delaware doesn't have nearly as many roads, so the total number is still fairly reasonable.
There may be some fixed costs per state. I don't know.
There is a risk that if Delaware got too little money, they could forgo it, lower their drinking age to 18, and have state liquor store sell to everyone under 21 in the surrounding states.
