I don't disagree with this sentiment, but it's worth pointing out that nearly all transportation projects from the "old days" around the world were done by private companies, and often met a swift end in bankruptcy. Creditors lost a lot, but the assets were then picked up by others, and refined through years of trial and error into endeavors of modest profitability. Only our sepia-colored glasses and the survival bias of remaining parts makes it look like people back then had it figured out, and we don't.
Private rail systems in Europe eventually were nationalized during the warring decades of the 1900s and remained that way longer than in the US, while in the US the government spun up Amtrak to relieve rail operators from passenger rail and its rapidly declining revenues, while letting freight railroads go through waves of mergers until only a handful remained. Soon after Amtrak, the airline industry was deregulated, and airlines proceeded to copy the idea: rack up costs, declare bankruptcy, sell, reset.
Truth is, big, ambitious construction projects, and big, ambitious service networks have always sucked, and the ones that remain went through many cycles of overruns and disappointment and service reduction before they stuck. Maybe what ought to worry us isn't that we've lost the magic touch of delivering ambitious, long-running deliverables (railroads, infrastructure, cities, government services...) sustainably, but that we never mastered it in the first place, and the things we have now are the much-recycled husks of former grand ideas that managed to eke by.