For concision, I abbreviate 'an answer that doesn't answer the OP' to NS, to mean 'non sequitur'.
I once asked on a Meta website somewhere (I forgot where, but please edit this OP if you find it) whether the existence of an answer to your question, correlates with the probability of receiving another answer. The answer was definitively positive: If your question received one answer already, then the likelihood of receiving another answer decreases with each subsequent answer
(ie: A second answer is less likely, a third even less likely, ...).
So how can NSs be removed, to ensure due attention and answers to questions that truly haven't been answered?
I already thought of, to no avail:
1. flagging for moderators' attention, either for the NS to be deleted or to be converted into a comment. However, I'm unsure whether moderators can do so.
2. commenting underneath the NS to raise this concern to the answerer, but the answerer may never edit the answer or comment.
3. downvoting, but this fails to remove the NS.
3.1. I personally eschew downvotes and never downvote on a Main site, because I prefer joyful, constructive criticism and positivity.
3.2. Even if I downvote, 1 lone downvote seems futile.
Moreover, an unjustified upvote for the NS would negate this downvote.