Because antisemitism has historically manifested as the scapegoating and demonization of Jews and the false portrayal of Jews as nefariously exerting power, and with things associated with Jews such as Israel and Zionism, so allegations of Israel committing genocide, and specifically comparisons of Israel’s actions in the Palestinian territories to the Holocaust or Holocaust inversion, were rightly at least initially taken with skepticism by many people aware of the history of antisemitism.
1) You think Israel hasn’t broken treaties? Be serious now. 2) entire wars were fought by Native nations to resist colonization. There was always resistance. 2) it’s odd as fuck to imply that capitulation to colonial invasion is a requisite to be protected from apartheid and mass killings.