Politicians are clearly incentivised by election, but saying its their only concern is generalising and reductionist.
The rest of your comment makes a lot of points, but broadly seems to assume that I'm claiming that private companies have no place in transport infrastructure, which is not the case. My point was that "the market" meaning an unmanaged build-it-and-they-will-come approach would not be optimal, in response to my parent commenter's "an easy thing for a market to fix".
Of course, public things like streets and roads and so on needs some planning. I'm no Ayn Rand "privatize all the things" guy.
But make that infrastructure flexible and less rigid and allow a city to adapt. The city where I live had 20K people 40 years ago, and was a logging/mill town. Now it's a tourist town with a budding high tech industry and closing in on 100K. Too much land use planning gets in the way of a city adapting.
Similarly... it's hard to impossible to predict the future, which is why economists predictions are so often wrong, as you point out. Gold rushes often ended in ghost towns. Who's to say in another 20 years your town won't be back doing logging and milling, and would be better off not bending to support an industry that may turn out to be ephemeral?
The item that worries me, and based on decades of observation, that the private companies will snap up all the profitable routes and leave the non-profitable routes to the city, thus deepening the budget gap.
The "market" will do that w/o some sort of regulation specifying that the private companies have to support the other routes.
Kind of points to the cable industry and local agreements w/ towns.