It's about need. Like yeah, Chicago through the Dakotas is easy as pie, but the demand would be to seattle and that crosses two mountain ranges and the only stops between Minnesota and Seattle with much demand there would be at national parks.

Like yeah it would be awesome as hell and the American version of the CCP would absofuckinglutely have a high speed rail to Yellowstone and the badlands since they're on the way. But Yellowstone is past the start of the mountains and you need to connect all the way to seattle for it to be more than a vanity project.

The important lines are the NY-Chicago (land is dirt cheap for lots of it, mountains are small, and population is dense with several makor cities you can hit) and the west coast line (basically actually do California high speed rail, then extend it from San Diego to just outside British Columbia. From there the east coast line, something involving texas, or stretching the ny-chicago line is good.