If there ever was a high-speed rail line out west that makes sense it would be the LA/San Bernardino to Las Vegas run, as anyone who has been on I15 on a weekend can testify. From Barstow on there would be little in the way to go around. Cheap, easy construction. So why hasn’t it been done?
Easy - it actually doesn’t make sense.
Although I wonder what it would be like if it was there all along.
You would probably have tons of people sitting in traffic on I-15 watching the choo choo go bye.