Please see this thread on the main Meta site: Problem with users not accepting answers
Accepting an answer is purely voluntary and there's no obligation to do so.
A lot of us participate here because we want to be helpful. If you're after reputation and green checkmarks, you might find it difficult to deal with the fact that there's nothing we can or should do to force people to vote or accept answers.
We already encourage voting and accepting answers via pop-ups, showing the accept rate on user cards, etc. Beyond that... it's all status-bydesign.