Looking at the questions with answers that have not been accepted, many of them are from the same 2-3 people.
In some cases people asking questions may be waiting for better answers. However in other cases good answers were made but never accepted.
How can we encourage people to accept quality answers to improve the experience of this site?
If quality answers are not provided then comments should be used to help address any confusion or answer deficiencies.
How can we encourage people to accept quality answers to improve the experience of this site?
Generally, you don't. The system already prompts users to accept an answer at an appropriate time, but accepting an answer is a completely voluntary activity, and it is up to the user to decide when (and if) they choose to accept an answer at all.
And please do not leave comments asking users to accept answers. It might seem like a harmless reminder of a feature a user may simply have forgotten, but the folks looking on will imitate what they see… so as the sites start to fill with "please accept an answer" and "can you accept my answer?", it starts to become somewhat noisy and annoying (and even a bit harassing) to just about everyone else looking on.
For the questions you are talking about leaving comments about the importance of accepting answers may help.
I do not think there is any good solution in cases where the person asks a question and never returns to this stack.
