Why do steam ejectors use steam instead of air or other gases?

[kaushal]

Mmmmm... why only steam is used in a steam ejector for creating vacuum and not anything like air or other inert gases...

 

[lalbatros]

I think air ejectors, N2 ejectors, natural gas ejector, and other types are also used.
It all depends on the applications and the environment.
Sometimes HP steam is easily available, maybe.
Sometimes compressed air is available.
Sometimes O2 is prohibited because of explosivity.
I don't know all the possible design aspects.

For further discussion, I think, you should give more details about what you have in mind and your reasons.