It has to do with the different histories of the charedi communities in the two countries. In America no one thought orthodox, much less charedim, stood a chance, due to materialism and everyone feeling like they had to work on Shabbos to survive. Only slowly did they gain a foothold and become dominant.
It was different in Israel because they old Yishuv of charedim came to Israel fully expecting to life a no-compromise impoverished life of Torah study alone. They may have even been escaping decrees in Europe forcing ill-intentioned secular studies on Jews. And then the same thing happened in Israel, people trying to force secular studies on them. So there was a big resistance. Here in North America secular studies was just pragmatic and was not seen as a big deal.
In addition, since the overall number of Jews is smaller in the US it’s harder to split into hard-and-fast camps. It’s common here (especially out of town) to daven in a shul with a mix of MO and Yeshivish, or some other MO/charedi mixture. It’s like a continuum in which a lot of people don’t even know if they’re MO or charedi or something in between (and they might label themselves differently than others do). It’s less likely that in Israel, where it’s easier to live in a neighborhood of like-minded people.
That said, there are more and more moderate charedim in Israel. But for geographic and historical and cultural (not to mention demographic) reasons the “extreme” charedi groups are also very prominent and growing.