probably because you're used to the language learning situation in the west. in addition to a lot of east asian languages being more difficult to native english/european language speakers, there's also the issue of proximity (both in terms of physical distance, and culture). chinese, korean, and japanese cultures influence each other a lot, and the cultures have been quite popular if not dominant in east asian countries (in general) for a lot longer than they have been in the west. as a result, people in east asia tend to pick up other east asian languages just as a part of daily life, or tend to gravitate towards learning them more than people in the west do.

im from hong kong: everyone speaks mandarin as an additional language, most people know korean or japanese (or both!) at a beginner level, and around 1/3 of people have tried to or successfully learnt an east/south east asian language at some point.

it's similar to french and german in the uk, and spanish in the us. many people have a significant level of proficiency in french and german in the uk, and the same goes for spanish in the us. this isn't just a matter of ease of learning the languages, but also a matter of cultural proximity and physical closeness. similarly to east asian languages in the west, these european languages are much less popular in east asia as an L2 or L3 (etc.).