It's a long story to even make sense of this topic, especially on why Chinese governments (not only CCP, but also KMT, and all previous dynasties) have such an obsession with controlling the Chinese language. But here are some interesting historical topics worth exploring:

First, according to the legend, the Chinese character was created by 仓颉[0] (2667 – 2596 BC, don't you love it when the four-eyed legend even has a birth year...), who is an official work for the ancient Yellow Emperor[1]. But the legends were well known to all the following dynasties, that an official invented the Chinese character, might give later generations the legitimacy and confidence to moderate it.

The Zhou[2] dynasty (1046 – 256 BC), which laid the very foundation of the Chinese culture, occupied the vast fertile land of China, with is on par with the EU in size. It's arguably the only feudal dynasty in Chinese history. The problem of feudalism is subjects would gradually gain power, so the country would break into pieces just like Europe, or the later Eastern Zhou. As China breaks, the need for diplomacy between countless independent Duchies and Counties was booming. On paper, the King of Zhou was still their liege, so it's very natural to leverage the dialect from the capital of Zhou, plus several classics like 诗[3] (the Poetry - the first book of poetry is, of course, called the Poetry). People call it 雅言[4] which means the language of elegance. It's a bit like Latin, which European always learn because of the Vatican, but people don't use it much in real life. If China continued this way it would be more like Europe and there would be many independent languages.

Then there's Qin[5] (221 - 206 BC), which was originally a subject of Zhou, but eventually became too powerful and unified China. Qin was very radical, it killed feudalism, and launched massive standardization like unifying administrative units, all kinds of measurements, and even the wheelbases (there were no train but they did anyway), and of course the Chinese Characters. It's doable because 1) Chinese is hieroglyphic, the character and the sound are not coupled 2) writing was still a practice of elites, and elites are fewer in number and can afford education.

As vast as China is, and as many dialects there are/were, people can always perfectly communicate with the written language throughout most Chinese history. Because of the hieroglyphic nature of the language, most of the characters from the Qin dynasty, still make sense even today if you know modern traditional Chinese and to a lesser extent simplified Chinese. (aka. The single-responsibility principle[6] in software engineering, the pronunciation, and the graphical representation are different reasons to change, so the decoupling makes the characters less screwed when the pronunciation changes). It's so powerful so that Chinese and Japanese may have some quasi-understanding to each other by writing Hanzi/Kanji. To understand what does a regnal year of Japanese Emperor means, people often have to go back to ancient Chinese texts - the most difficult part of the Japanese and Korean for western people, sometimes are easiest for Chinese.

And for the following millenniums, those practices almost became a tradition: the dialect of the capital of that time would be the official language. And from time to time there were attempts to unify the vocal dialects during dynasties, but it was too hard because how people speak was always changing, until modern days that Guoyu[7] and Putonghua[7] could achieve the impossible through technologies.

So: 1) The language is not only seen by governments as a tool of communication but also a tie that binds everything together - loosening that tie might come with risks. 2) It's more or less a tradition so there are substantially fewer pushbacks than other countries, and legitimate Chinese governments throughout history see no reason to not leverage that.

[0] https://en.wikipedia.org/wiki/Cangjie
[1] https://en.wikipedia.org/wiki/Yellow_Emperor
[2] https://en.wikipedia.org/wiki/Zhou_dynasty
[3] https://en.wikipedia.org/wiki/Classic_of_Poetry
[4] Unfortunately, there's no English translation to this Wiki yet: https://zh.wikipedia.org/wiki/%E9%9B%85%E9%9F%B3
[5] https://en.wikipedia.org/wiki/Qin_dynasty
[6] https://en.wikipedia.org/wiki/Single-responsibility_principl...
[7] & [8] https://en.wikipedia.org/wiki/Standard_Chinese