the point of yidish was to create a different language from the goyim.Just like we are proud to dress differently our names are different the same is with language.Apparently not everybody was fluent in LAH”K at that time and at the same time they wanted a language that would still resemble the one spoken in their country of residents so they would be able to communicate.Once ppl got used to that language it remained the first language to many jews as it would be hard to create one in every country.Hence it is as if we would create a revised version of english to be different and still be able to communicate at the same time.But we do see kabbalistic explanations of yiddish words in sifrei chasidus proving that there’s a deeper meaning behind this language.