Different people seem to have different value systems. The "costs" involved may not concern Xi all that much, provided he "wins".
Hell, we've got genuine believers (...or shills) even in these comments talking about how US support for Taiwan is all just a ploy to weaken China.
If Xi makes a move on Taiwan, he turns China into a Russia-like pariah to the West and bears an immense cost in lives and materiel. For what gain exactly?
Taiwan is worth more as a bogeyman he can point to for nationalistic rallying than as an actual possession.
How do you measure gain? If consider only economic benefits, why did Putin attack Ukraine?
Now if you consider that these men have big egos, are more driven by nationalist motives than economic ones and that they want to go down in history as the next Peter the Great or Qin Shihuang?
Then maybe they are willing to tolerate that their peoples experience a period of economic decline, to ensure the greatnest of the nation and the supreme leader?
Given their value systems, this may even be rational.
Deng Xiaoping brought Hong Kong and Macao back, but he was memorated as a great leader not because of this, but because he opened the door for China to its economic prosperity.
Xi needs to take Korea and Japan too?