It is convenient. By claiming unwavering support for Israel you can distract from your own antisemitism and blame it on brown people. This comes in especially useful to ramp up racism against the very same people you blame for your own antisemitism.

Israel plays along in this game, as they profit both from racism against brown people letting them get away with more crimes as well as profiting from cases of antisemitism, as it allows Israel to claim it is needed for Jewish safety.