Have we solved all human rights issues so we now moved on to grant animals personhood?
While I'm not disagreeing with you, I really dislike this question. Have we solved all problems on Earth that we should start exploring space? Have we solved all problems in America so we should start developing a foreign policy? Have we solved all problems in physics that we can now move on to chemistry?
Simply put, we don't have a clear queue of problems, and probably never will. And even if we did, not all problems can be solved faster by having more people work on them, so it will always make sense to be working on multiple problems at a time.