But not all factions would use them. Even some nations that were around the area didn't use them, or we at least have no sollid proof for it.
For example, Parthians have no solid proof for using elephants, but their successors, the Sassanians did use elephants.
And why would the Romans be able to use them? They owned North Africa, and they didn't use elephants.

But you can always recruit elephant mercanaries.