On the WPSE question referenced, the OP had (and still has) a zero percent accept rate, out of ten questions asked.
(Edited to add: of those ten questions, multiple questions have answers that the OP has indicated, via comment, to be correct, and to which WPSE users have replied with further comments instructing the OP to accept that answer - and which the OP still refuses to accept.)
Currently, WPSE has several such users. The problem would be more isolated if the site were more mature, but as it is, a small number of such users has a disproportionate impact on the overall quality of the site. To me, these numbers are indicative of:
- A user not caring enough to understand site mechanics to accept answers, or,
- A user who asks so many poor-quality questions that cannot be answered reasonably
Clearly, accept rate is intended to be used for some purpose, or else it wouldn't have a place of such prominence in the UI.
Taking the course of simply ignoring such a user doesn't help anyone. The user is potentially frustrated that none of his questions get answered. Community members who make a good-faith effort to answer his questions are frustrated when their correct answers are not accepted. The overall quality of Questions and Answers on the WPSE site is diluted by unanswered and/or poor-quality questions.
Thus, the only other course of action is for the community to attempt to encourage/instruct users in proper site mechanics, including accepting answers and asking high-quality questions. One means of such encouragement/instruction is commenting on users' accept rates.
Note: I generally only leave such a comment if the user has asked at least 10 questions.
Also, I generally try to follow up such a comment by perusing the user's previous questions, to see if any can be improved, or if any can be easily answered. Quite often, such perusal reveals several questions that are off-topic, not constructive, too localized, or not a real question. Occasionally, a good question will remain unanswered. I do my best to answer such questions, and then if/when the OP engages with the answer, I leave a comment regarding how to accept an answer if the OP considers it to be correct.