Joseph,
Two reasons: 1. I think in recent years people have started to take the “leader of Klal Yisroel” idea too literally. As if there was an actual rabbinic position with that title (like the Naasi in Mishnaic times).
2. Properly understood the question is non-sensical. The authority or authorities of the yeshivishe velt come about organically. There is no appointing body, no formal vote, no particular criteria. You can’t really ask the question as if there can be an immediate answer. You just need to look around after a while and see who the rabbonim you follow defer to.
To bring my point home. I did not think Rav Shteinman tz”l was the “Leader of Klal Yisroel.” I saw large segments of the Yishivish velt not deferring to him. And I did not get the impression that people viewed him as a halachic authority.