One thing that makes Esperanto popular in Asia is that the Asian languages are much more dissimilar than European languages. For example, the effort for a Japanese person to learn Korean is much more than to learn Esperanto.
Try eg. Japanese<->Chinese or Thai<->Malay for neighboring but completely unrelated languages.
Even though it's grammar is different, China had a huge cultural influence on Japan, and both its writing system and its vocabulary (as spoken over a thousand years ago though!) were imported and incorporated into Japanese. Something like 60% of the Japanese dictionary is Chinese-derived either as old imported words, or more modern "wasei kango" (lit. Japanese-made Chinese words) -- think "television" for an English word equivalent (modern idea but coined with Greek and Latin word roots).
There's a lot of really interesting details about this on Wikipedia here: https://en.wikipedia.org/wiki/Sino-Japanese_vocabulary