That’s interesting.
Rav Elchonon Wasserman and many others all write explicitly that Nationalism/Zionism is idolatry and that Torah and, liHavdil, Nationalism is Torah and idolatry biShituf. The Brisker Rav published, and the Gerrer Rebbe and others signed on, that “Dati Leumi” education is a “sea of heresy mixed in with a drop of Torah”.
So, perhaps a better question would be why anyone would possibly follow these grotesque distortions of Torah (Zionism of any flavor) rather than simply following liHavdil only the Torah.
To be fair, though, the reason that ZSK isn’t likely concerned about L”H against Conservative and Reform communities is that ZSK likely agrees that those movements are heretical and that its followers are unfortunately not biChlal amisecha.