While the majority of Jews worldwide may be Ashkenazim, the majority of Ashkenazim aren’t frum, and I suspect the number of non-frum Yiddish speakers is rapidly declining. That means that most Jews don’t know Yiddish. OTOH, neither do they know Hebrew.
Vochindik, a major reason Yiddish speakers “have a leg up in learning Torah” over chiloni Hebrew speakers has nothing to do with language. If you have background knowledge, learning is easier than if you don’t.