Why do people ask a question on Yahoo!Answers and then disappear with out selecting a best answer

In my case, for a while I didn't know I could pick a best answer. After I found out about it, I checked the answers for a best one but usually there is no best answer. Sometimes there isn't even a right one so I don't always choose.

If you ask a question and you don't like any of the answers why should you select a best answer?

You might perhaps prefer to wait until the question goes to the voting community and then you can vote for the "No best answer" option.

I think that once they get an answer to their question, they just move on to other things or maybe they just don't like using the site. It might be kids, and their parents block the site after they see some of the other Q&As here.

Maybe their account got deleted. Yahoo suspends a boatload of accounts every week.

I woder this at times. I have got quite a few BAs because of voting, & somehow it doesn't seem as good as if the asker awarded you the 10pts.