in China, it's likely about not setting precedent for sub states seceding, making the country less powerful because smaller, as well as making the "communist" setup look weaker/optional. Are these the same as 1984? I don't know.
In many ways this can be compared to the purpose of war in the feudal middle ages where land always needed to be conquered to be given as fiefs to up-and-coming nobility so that nobility would support the current king in his strive to remain in power. Things change but the basic tenet stays the same: those in power want to remain there and will use the means at their disposition to do so.
Wanna maybe expand on the point you're trying to make?
So it’s not just national pride, there is a huge strategic element at play also.
It's much more important than submarines. Their trade, and access to resources such as oil, goes through that territory controlled by others (the US especially).
There is simply too much nationalism and national pride locked up with the whole South China Sea and Taiwan that no amount of logic and truth can change how it is perceived in China.
The South China Sea dispute has nothing to facts like these, and all about geopolitics and power within China. Like with the Austria pre-ww2, if the Chinese were to invade and conquer Taiwan and control the entire SCS, they'll magically find other "distractions" and "conflicts" to distract people away from their own misrule and corruption.
With Putin's Russia and the CCP, there must always be enemies (both internal and external). If they don't exist, you create one (think FalunGong)