"word" isn't a useful concept in a lot of languages. Words are obvious in English because English is analytic: https://en.wikipedia.org/wiki/Analytic_language

But there are tons of languages (not just CJK languages) that use either compounding or combos of root + prefix/suffix/infix to express what would be multiple words in English. E.g. German 'Schadenfreude'. Its actually way more useful to tokenize this as separate parts because e.g. 'Freude' might be part of a lot of other "words" as well. So you can share that token across a lot of words, thereby keeping the vocab compact.