Well, the post isn't that
old. Anyhow, both readings "why" and "what" are possible. If my key had been designed with learners in mind, I probably would have gone for the "what" translation, which is what the author probably expected the learner to choose. Since, however, I answered the questions with the intent of impressing my teacher, I of course went for the more obscure answer of "why"
flebile nescio quid queritur lyra, flebile lingua murmurat exanimis, respondent flebile ripae