Viewed through the lens of the original Silk Road, the "closing off and turning inwards" trend is consistent with an increasingly Middle Kingdom posture. China is the center of the world in this posture, and in a very nearly literal sense all roads lead to China with BRI.

It also neatly dovetails with asserting greater, more finely-granular political and social control the leadership desires (from which all other power emanates in such a world-view). Chinese nationalism is strongly encouraged, and evolving it to a "New Middle Kingdom" posture will generate incredibly powerful historical resonance with Chinese.

Convincing 1.4B people to politically turn inward to only concerning themselves with domestic matters because China is the only nation that matters in an exceptionalism narrative, while delivering a practical logistics network to feed their ramping up resource requirements (because China cannot sole-source these resources domestically), could be a winning formula for a leadership that wants to maintain the bargain they have struck with the people: continued increasing prosperity in exchange for continued Mandate from Heaven.

This is just my uninformed perspective from the outside looking in, without extensive corroborating data and cultural referents. I welcome discussion on what is really going on.

You’re right, it’s an uninformed perspective. You’re starting with a conclusion of what the Chinese government’s intent is and then trying to find a way to fit the facts into that narrative.