Software is more like a Ship of Theseus in a way that roads are not. That is, the cost to "switch out" one version of software for another is effectively zero,

Software is more like a Ship of Theseus in a way that roads are not. That is, the cost to "switch out" one version of software for another is effectively zero, so if makes sense to "maintain" the product in perpetuity. For a road and other capital expenditures with heavy dependencies, your "lifecycle" is As few changes as possible; and then, all of it changes.