There's small matter of the gigantic trove of treasure.
The Kuomintang took huge amounts of priceless Chinese artifacts when they fled to Taiwan, which are now in the National Palace Museum[1]. There's a case to be made that the CCP was on an iconoclastic spree and there was good reason to take the artifacts to Taiwan for safekeeping, but the fact remains that vast amounts of priceless Chinese relics are now in Taiwan. China would like them back and is willing to do more than ask politely. Taiwan can blow up the fabs, sure, but they're probably not going to blow up the relics. Chinese leadership would gain a historic amount of face by bringing them home.
I'd say a reason, not necessarily the reason. Taiwan rubbed China's face in it for decades, it seems like a long-held grudge:
> During the 1960s and 1970s, the National Palace Museum was used by the Kuomintang to support its claim that the Republic of China was the sole legitimate government of all China, in that it was the sole preserver of traditional Chinese culture amid social change and the Cultural Revolution in mainland China, and tended to emphasize Chinese nationalism.
Even though, if you read further down in the article, there's not as much acrimony about it in recent years. Still, China has had dreams to invade Taiwan for decades, mostly for nationalist reasons, and this is likely one of the reasons that's higher in the list.
The Kuomintang took huge amounts of priceless Chinese artifacts when they fled to Taiwan, which are now in the National Palace Museum[1]. There's a case to be made that the CCP was on an iconoclastic spree and there was good reason to take the artifacts to Taiwan for safekeeping, but the fact remains that vast amounts of priceless Chinese relics are now in Taiwan. China would like them back and is willing to do more than ask politely. Taiwan can blow up the fabs, sure, but they're probably not going to blow up the relics. Chinese leadership would gain a historic amount of face by bringing them home.
[1] https://en.wikipedia.org/wiki/National_Palace_Museum