Vacuum is mean. It's difficult to maintain it even on the small scale.
Having the tube, 500 km long, without any failure caused by anything from the fatigue of the material, landslides, faulty electrical system is difficult to imagine.

And imagine the emergency. Hyperloop is traveling 1000 km/h and it needs to be stopped.

1g de-acceleration from 1000 km/h: it needs 4 kilometers to stop! (no delay in decision making included). It also takes 28s.
Any failure in the next 5km - and all the passengers are dead or injured.

And the energy required to stop it would be incredible to achieve in practice.