If Ego functions cannot be used then work usually feels boring. Its difficult to give any other reason. The translators I know are usually either intuitives or logical types.
I've talked to other SEI translators and they don't really like their job either. And the reason SEI is picky about the job is because they happen to have Ego functions that are hard to put to use in society. They are not more picky than other types, really. Its just that it's more difficult to find a job that matches their Ego. That's what all types are trying to do.
I currently work in a low-status job as a painter, and it gives me much more satisfaction, mentally, because there is actually constant use for Si, and that's rare in other jobs.