You theoretically could, but since water is incompressible, you get arbitrarily high pressure for free in a sufficiently strong pressure vessel assuming zero ai

You theoretically could, but since water is incompressible, you get arbitrarily high pressure for free in a sufficiently strong pressure vessel assuming zero air content. Doing the same with air would require a lot of energy and an intricate feedback loop. Beyond that: compressing air causes it to rise in temperature, which further complicates things.