Why do some people say they are East Asian instead of specifying that they are Chinese, Japanese, or South Korean?

More and more people are starting to do this, but a Chinese person is a Chinese person, a Japanese person is a Japanese person, and a South Korean is a South Korean.

Each country has a different history and culture.

What is even more ridiculous is that people who do this love to speak on behalf of all East Asians. It is the same as a German speaking for a French person just because Germans and French people are both Western European.

The international achievements of Chinese people, Japanese people, and South Koreans are the achievements of their respective countries and have nothing to do with the other two.

Calling yourself East Asian makes is seem like you want to be part of all of it.

Are the people who call themselves East Asian Southeast Asians of Chinese descent or Americans of Chinese, Japanese, or South Korean descent, or are they actually from China, Japan, or South Korea themselves?