Australia

The reason road trains exist is to make trucks more efficient than normal trucks by transporting in bulk - instead of carrying the weight of multiple trucks + cargo, it's only one big truck. More efficient, and therefore cheaper.

Rail is even more efficient than road trains at transporting in bulk from region to region, as they don't waste energy on friction, and are even better at carrying in bulk. Road trains don't exist in most countries because they usually have rail to take its place, trucks have their niche in the first and last legs within small regions. After all, moving a truck across regions is less efficient (and therefore more expensive to do).

The only form of transport more efficient than freight trains are cargo ships, which can't go inland. There's a reason mining companies often build their own freight railways to transport between mine and port.

Australia is finishing a build of Inland Rail, a rail freight corridor right now. I'd hardly call it dead when we are expanding the rail network. Admittedly the initial build is over budget, but the initial build is always the most expensive part.