Rails don’t last hundreds of years. They just do the regular disassembly and replacement tasks at night in a rolling fashion that they look permanent to users.

It’s expensive to be poor.

Like poor people can’t buy bulk, real countries with limited budgets can’t spend freely for a 100-year project. It will be well worth it in the end, but you have to pay it all now.

If you think 'last' means lay down the tracks once and be done with it, you're wrong. To be really usable they need constant maintenance, no matter if freight, or high speed rail.