Why is this site shutting down, or being sold to someone else?

For the umpteenth time: Because Verizon Media is choosing to shut it down (just as they did Yahoo Messenger and Yahoo Groups). No specific explanation was given, but considering the significant decline in quality of content on the site versus the cost of cleaning it up and keeping it running, it's not a surprise (a disappointment, but not a surprise). Do you really think this question hasn’t been asked dozens of times already? One need only review the question list to find the responses.
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You can do a search on question and answer websites, and some suggestions come up, including links that list the best or most popular ones (there are a number of them). Each user will have to decide for themselves which, if any, to use. Everyone likes a different type of site. Some will be better moderated than others.

Yahoo Answers has not been doing well Lately a lot of Users have Left Poor Maintenance of the
Site they have not Fixed a lot of the Problems they are Likely Losing Money on it as well so
They feel its Best to Close it Down If there not going to Fix it they minus as well Close it
Down

And Yes there are other Sites you can check out Quora or Redditt 

similar, but not equal. anyway the most similar are quora and reddit.