Saying “Eretz Yisrael” shows rejection of the zionist government, either because you hold the establishment of the secular “Medinat Yisrael” violates halacha, or because you reject the position of the zionists that “Israel” consists only of the territory over which the Medinah claims sovereignty, excluding (in particular) the West Bank. Therefore both anti-zionist Hareidim, and “fanatical” Religious Zionists both have good reason to refer to “Eretz Yisrael” rather than the medinah (“Israel”).
