Why does it matter if the same question is asked twice? Sometimes the second question gets better answer.
That's a good question, but it's been asked already here on Mi Yodeya Meta. Now, suppose this answer I'm penning is unclear to you or incomplete. Wouldn't it be better for me to write it as an answer to the older question instead, where you can read preexisting answers also, and to link you there? And wouldn't it be better for future readers to read all the answers in one place? And if my answer duplicates those answers, then isn't it a shame that I wasted my time writing it up instead of (when reading your question) being redirected to the older question where I could see that my answer already existed?
Now, sometimes the newer question is not the same as the older one, but is very closely related. Then it should not be closed as a duplicate. But where it's the same question, it's in everybody's best interests to be redirected to one question that collects all the answers.
If you're worried that the older question is insufficiently well answered, and are therefore duplicating it on purpose, see "What should I do if no one answers my question?".