Its literally just not worth it, all while being stunningly dangerous. When a zero pressure vacuum ruptures, it violently contracts, generally crushing itself.

This will require a zero pressure vessel as wide as a train, that is hundreds or thousands of miles long to be viable. One hole in the thousand mile line will shut the whole system down while it's repaired and then depressurized. This strands any other trains in the tunnel until this is done, so your "superspeed" tunnel is really super slow. Even if they have some kind of "safety valvue at set intervals that means the whole line doesnt go down on pressure gain, you still cant use the rest of the line.

So for this to work, you need multiple redundant tunnels, all of which can be taken down by one person with a gun at any point along a long, long track.

So you can spend just endless billions, literally hundreds of billions, making these redundant train tunnels that still aren't redundant, or you can spin up 10x-100x as much HSR that goes 300km and actually interlink the country with truly redundant and fast transportation.