Maybe he kept his identity secret because he did not want his daily life disturbed. We know how famous Bitcoin is now and if we know who the inventor is, there will be many journalists every day who come to question him. Always visited by journalists is not fun, especially now that many journalists who always dismantle the secrets of people.
Stop it.
He had no idea it would be this popular. The people who's shoulders Satoshi stood on weren't in any way beating off crowds of people or receiving threats for what they created. So he had no reason to believe he would be threatened by the paparazzi or evil doers. He likely envisioned bitcoin to be somewhat as popular as Second Life Linden Dollars which had well under 100K users at the time of Bitcoins release.
Satoshi established the pseudonym for one reason. He was avoiding an "intellectual property" claim from his employer. He did not want his employer to be able to control a protocol that was supposed to eliminate "third party trust".
Say Google made a claim that the bitcoin code was theirs because the inventor was working for them at the time. Nobody would have used it as it couldn't ever be used for what it truly was solving. Google would have used it likely in the GoogleSphere for payments on Android and the likes but it wouldn't have become what it is as Google would end up being the "trusted third party" bitcoin was trying to eliminate. Sure Google would get brownie points for having an "open ledger" but mining would have been eliminated and each token would be backed by the word of Google making your digi-cash stash safe yet easily used and verifiable.
I use Google as the example because I believe it was Google who Satoshi was hiding his identity from. And this is why I believe Mike Hearn is the real identity behind Satoshi Nakamoto.
https://bitcointalksearch.org/topic/could-satoshi-nakamoto-be-mike-hearn-2146520If you actually think about real life reasons Satoshi would hide his identity and not make believe fantasy crap that he somehow knew Bitcoin would be this big and his life would be in more danger than the other thousands of billionaires out there, you would likely come to the same conclusion about why he hid his identity. You may not come to the conclusion of same person behind it as I have but regardless of who, the reason is pretty clear.