The "replaceable" nature of the translator is the key. As long as publishers can easily get a different person to do the work with little effect on the success

The "replaceable" nature of the translator is the key. As long as publishers can easily get a different person to do the work with little effect on the success of the piece, translation compensation will be low. Yes, it is a creative effort. Yes, an excellent translation (especially of poetry!) is difficult, and is a much better final product. But if the translator's name doesn't drive sales, translators won't be compensated as if it did.