Yes, but when two customers on your 50-household backhaul use half the total bandwidth, then you either have to pay to install more, or force all 50 users to deal with network congestion issues.
To put it in terms of your road analogy, tractor-trailer rigs use more highway space than autos, and they also increase maintenance costs dramatically. That's why your average rig may pay as much as $15,000 a year in annual road taxes, far more than the fee for one (or even ten) cars. You use more road, you pay more.