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There is one reason: If you think bitcoin is some kind of pyramid like scam he is going to make a lot of money from it. As the creator he was able to accumulate many bitcoins while mining was still easy.

Isn't curiousity enough?

When people like a creation, people also want to know about its creator(s). See also: Steve Jobs.

Because people want to tear apart the fact that, essentially, Anonymous writes code. They can't leave it alone.