For the same reason we don't refer to Hitler as a socialist. There are still places with actual communes.
Words have meaning so unless you're using them as a proper noun or acronym (CCP, NAZI) you follow common usage. Just because a word is useful for demagoguery or insult doesn't make it correct.
Extraordinary claims call for extraordinary evidence.
The CCP has been around for about a hundred years, founded in 1921. They haven’t changed their name in almost 100 years.
“Officially, the CCP is committed to communism and continues to participate in the International Meeting of Communist and Workers' Parties each year. According to the party constitution, the CCP adheres to Marxism–Leninism, Mao Zedong Thought, socialism with Chinese characteristics, Deng Xiaoping Theory, the Three Represents, the Scientific Outlook on Development, and Xi Jinping Thought. The official explanation for China's economic reforms is that the country is in the primary stage of socialism, a developmental stage similar to the capitalist mode of production. The command economy established under Mao Zedong was replaced by the socialist market economy under Deng Xiaoping, the current economic system, on the basis that "Practice is the Sole Criterion for the Truth".”
Not saying your anecdatum isn’t correct, but it’s a higher hill to climb than that. If someone described a person to me as the description above, I’d say “Gee, that’s most likely a communist.”
The Nazi party was founded in 1919 and ended, rather spectacularly, in 1945. That’s only 25 years.
This is an old, stale debate. The common usage of the word "communist" is defined not by vague Marxist theorising or tiny enclaves nobody has ever heard of, but rather the typical end state of actual communist revolutions. That's how the word is used in practice.
This has the unfortunate property that at least for China the end-state is constantly evolving, but only in relatively unimportant ways. China has a freer market than the USSR did, but even the USSR had to abandon completely planned economics almost immediately after Lenin took power. After that it was mixed, just like China's. And in all other ways they are the same: no democracy, rampant censorship and propaganda by state-allied corporate entities, no real private property rights (if you can lose your IPO by giving a single speech criticising the government, it's fair to say whatever private property rights you thought you had don't really exist).
Why? China was clearly a communist project, and this is what they became. Why is the end result we see in reality less valid than the theory?