Competition fails where the cost of redundancy is prohibitive, which leads to either large scale partitioning (local monopolies) or monopoly (global monopoly).

Competition fails where the cost of redundancy is prohibitive, which leads to either large scale partitioning (local monopolies) or monopoly (global monopoly). It doesn't really make sense to build several rail lines connecting city A to B. The same goes for telephone lines -- in all but the most dense centers, the infrastructure cost is so dominant that redundancy doesn't make sense. Now for mobile data for example, you can, for a more modest investment, cover large areas with cell towers, so direct competition occurs.