Dave died years ago following depression, before releasing bitcoin he published papers on the topic of Cipher Block Chaining and similar cryptographic tech: https://www.davekleiman.com/
This has already been known for years. There were good reasons to keep his anonimity at the time, especially if you consider that his main customer was the same government where cryptography tech is considered an ammunition. At that time he could face jail for his work, or in the best scenario lose his customers/reputation.
You have to remember that in 2009 and next years, BTC was something only relevant for cybersec researchers and criminals. You would not want to be seen as associated with the latter.