It’s not really feasible to separate noble gases out of the atmosphere in a building HVAC system.

Couldn't you just use positive pressure of O2 and nitrogen? Push all other gasses out? Would cost a lot but it is doable.

More recent tools do work that way. The whole "tool line" is flushed with process atmosphere.

Probably the buildings are so big nowadays that it's geometrically impossible to have farms nearby the actual plant.