Why do most YA users that asks questions fail to pick a Best Answer?

Because they do not know how or ask the question less than one hour and forget to go back after one hour to choose a best answer

I read your answer and instructions on how to award best answer; which I did. At the same time I commented to my own question with a follow up of sorts thinking that you might have an answer to my comment which was still on point about my account being unavailable for me to access especially since the apparent closing of the acct did not fit your explanation. I thought perhaps you are one of the Yahoo volunteers and might help me resolve the issue.

That said your original answer still sounds right and maybe you don't know the answer to part 2

because they always have.....most people who ask don't care what they're supposed to do on this site once they have the info they needed so most Q's just stay open.

That's why Y!A USED to have voting, as a way of other users having a chance to resolve questions the askers had abandoned. But of course now that's gone barely anything gets resolved anymore

Because they forget about the question, are too lazy to pick, don't know how to select a BA, or can't choose one.

I always do. Unless there are no good answers. Head over to the politics section. Many there do.