a brilliant coder found out that he had few years to live, the only thing he was concerned about is how he could provide for his family before his death. So he put all those years of computer skill into developing a financial system with the hope it would be of value for the sole purpose of leaving something for his beloved ones.
the guy passed away of ALS and his project turned out to leave a fortune for his family and making alot of people millionaires.
why did he keep his identity a secret? imagine him going out as Hal Finney, his legacy would have been his family's nightmare with all people wanting a piece of his god-knows how many bitcoins.
Hal died with the Satoshi he created. Watch breaking bad to live this drama and leave it at that.