[Nyororin]

I recall there was some sort of mini-documentary on a few years back looking into where this came from.

I seem to recall that one of the first major textbooks for learning Japanese in China used "である" on the end of every sentence, and often forgot the で, leaving あるよ as a valid and preferred casual ending.

I believe it was quickly corrected, but it stuck as a stereotype of Japanese learned from Chinese textbooks.