Why haven't Jews had a consistent language throughout history? What was wrong with Lashon Hakodesh (besides for learning the local language)? We adopted Aramaic with a mixture of LHK and local variations of this such as Judeo-Arabic, Ladino and Yiddish. Was this conglomeration of LHK and the local language by intent? A new language seems to be forming which is known as yeshivish. Though I'm not sure if that falls under the same category as the previous languages listed. Any thoughts?
I mean they kept their language throughout 210 years of slavery in Egypt (see Vayikra Rabbah 32) does that count as "consistent".
The other instances you cite such as Yiddish, Ladino etc. are a product of living in galus, where they maintained elements of lashon hakodesh but also had to adapt their language to the countries they were living in.