The problem is not cutting a switchback in a mountain side, but building superhighways or roads through properties belonging to people who don't want those roads built. Things don't always scale up easily.
- Multiple roads.
- Tunnels.
- Bridges.
- Passing around
- Using secondary identities to buy the land secretly.
- Buy more than the strictly necessary land and profit from the valuation of adjacent land now better connected.
- Railroads.
- Free-market collective transports (cheaper, more frequent).
- Free-market airports, perhaps built by airlines themselves - there would be many of them.
- No cumbersome airport regulations nor TSA, speeding up boarding time and bringing the price down. Perhaps planes would become more practical than buses/trains even for not so long distances like 200km or so.
- Etc etc etc.
As you can see, there are many solutions to the "problem" you raise. And I'm just an ordinary guy, with no particular experience in the field. Imagine what millions of people competing freely would be able to build.