Besides this, Satoshi seems to have had quite a few reasons to develop
Bitcoin such as fleeing from banks, creating a trustless system, etc.
OK. So my reason is to protect your life savings from this ponzi scheme called bitcoin

I want to prove that decentralized trustless system can not exists in long term.
It either transforms to centralized system or loses its security.
Since you're giving me valid advice, I'll give you valid advice too: don't put all your eggs on the same basket

As for long term decentralization, we'll see. The system may fail, but competition may rise and prove to be even more up to the task (that's why some testing is important too).
Problems will eventually find a solution where there is a need.
