No one has ever made a vacuum tube 600km long with a cross-section of over a meter. Much less one that has to maintain vacuum with a super heavy train going at 400m/s. This is at least an order of magnitude more difficult than anything of the same nature. It's really not comparable to anything in existence. CERN is a Tonka truck by comparison.

Burying the lines would already make it an order of magnitude more expensive than what was promised. And now you have to compensate for ground movements, since your tube is fat and hundreds of kilometers in length, which makes it even more expensive.

Insulating the tubes to maintain temperature would be incredibly costly, and if there ever was a failure or natural disaster that prevented you from keeping up the power need, your tube will break.

Materials that have such little temperature change coefficients are much too expensive to build a 600km long multiple meter wide tube with.

If you allow the tubes to change length, your stations will move, sometimes in unpredictable directions. You also risk gigantic stresses caused by temperature differentials causing bending forces.

Vacuum expansion joints of that scale, for such a length, with such reliability are literally unheard of. And would likely be insanely expensive.