Look, stop trying to overthink very easy business decisions.
The current SIE is a merger of the Japanese SCE and the US Sony Networking departments. The networking department is responsible for this like PSN.
PSN is making Sony a ton of money. So logically, the move was sound.
Likewise, the Japanese game market is moving further away from console experiences, and the USA is very much a strong market with growth potential for the PS brand.
It's that simple (when reduced to very basic form).
Totally agree plus it's where most of the big Sony studios are.