If you change inputs then obviously you will get a different output. Crucially using the same inputs, however, produces the same output. So compilers are actually deterministic.
Having faith that determinism will last forever is foolish. You have to upgrade at some point, and you will run into problems. New bugs, incompatibilities, workflow changes, whatever the case will make the determinism property moot.
The reason is, it's often more work to be deterministic than not deterministic, so compilers don't do it. For example, they may compile functions in parallel and append them to the output in the order they complete.