Ok, so I built a road between two adjacent communities. What stops someone else from doing the same with a slightly different route, or heck, right alongside my road? I'm genuinely curious.
The fact that if I built my road first, it's logical that I also built the cross-connections to other roads and towns. So how do you propose to build your second road alongside mine without crossing or connecting to it
This isn't a hard scenario to imagine - look at any random chunk of road in your neighborhood, imagine the roads are privately owned (by folks hostile enough to you that you're trying to build your own), and for the sake of argument, give yourself infinite money - enough to buy whatever lands and right-of-ways you need, but not enough to buy out the Evil Roadowner you're competing with.
Now, where do you propose to run your Alternate Road System?