It’s mostly a question of cost. High pressure systems are only economic if they transport far more material than they leak, but some minor leaks are fairly trivial. If you talking coarse aka 7,600 micron aka 7.6 torr aka 1% atmospheric pressure you gain most of the value moving a train through an evacuated tube while still being able to use cheap and very fast pump systems to deal is lots of slow leaks. Making that kind of a vaccum tube even easier to maintain.

The LHC however deals with high vacuume becase they need particles to travel hundreds of miles without encountering any atmospheric particles. That would let trains reach orbital velocity without issue, but would be horrifically expensive.

Basicly 100% to 1% vacuume is considered rough/coarse and it cheap. 1% to 1 micron is the middle ground which is increasingly difficult but still not that bad. Under 1 micron aka High vacuume is expensive and mostly the realm of science experiments.

https://www.hydraulicspneumatics.com/200/TechZone/Vacuum/Art...