Does the "Cloud" run on physical servers in datacen

Nitrogen/oxygen air isn't free to make; you've got to have a star fusing all that hydrogen into heaver elements and then you've got to extract it from the star (usually by blowing it up) and then you've got to actively keep the oxygen in the atmosphere because it wants to combine with carbon and other elements.

So yeah, it's just like thin air; it's incredibly hard to make and keep available, but doing so just isn't your problem.