why then did he decided to move on to other things instead of focusing more on the Bitcoin project to make sure that he also took part in achieving the adoption of this digital currency?
Satoshi created Bitcoin in such a way that the network no longer needed him, he played his own part before he left this decentralized network. I don't see anything "unfortunate" in what Satoshi did, he created a p2p cash system for people who wanted to control their finances, and made it in such a way that it is the community itself that makes its own decision and not the creator or any central authority. Satoshi may be dead by now, or maybe he did move to develop another project, whichever it is, he has already done so much for lovers of decentralization.