New users often assume that they are the first to ever encounter a given problem / think of a given feature / etc... And so they don't bother searching. (Contrast this with old users, who know that others will do their searching for them if they post a question...)
Sometimes they do (But see #1). However, in many cases a question will be asked many times in many different ways, with no easy similarities between titles (and to be fair, many titles are horribly bad at describing the actual question). Closing these as duplicates increases the chance that search will work better in the future (for users that bother to use it).
This may look a bit odd, but it's normal - Meta is all about