AntiZionism originates in the Soviet Union so it’s always been a lefty thing, so it got a head start there. Because of this it’s always been mixed in with anti-capitalism, anti-westernism so it’s found a naturally home in the modern progressive left and its simplistic oppressor-oppressed anti-western narrative. Add in millennia old anti-Semitism ( Jews seem to suffer from being successful enough to notice but so tiny in number most people don’t know any Jewish people, so they are easy to dehumanize) and you have a perfect storm for the our age’s hate movement : antiZionism.
What the ‘Gaza’ movement most certainly is not, is a human rights movement. As you point out yourself OP, there is no movement for genuine modern genocides such as Sudan ( in fact when Gillian Anderson tried talking about this she got hated on by the ‘pro-Palestinians’. ) and the inhumane reaction ever since Oct 7th where the pro-Pal movement has denied or tried to erase the sadistic atrocity against Israelies. Nor does the self-identified pro-Pal movement want to condemn the atrocities committed against Palestinians by Hamas, or condemn them for failing to protect their people in the underground city they built of hundreds of miles of tunnels in two layers. I could go on.
So to answer you question, the answer is not ‘why Gaza’ , as this movement is really an Israel hating movement. AntiZionism is a modern hate movement.
And yes, it’s the modern ages jew hate movement. It started off in anti-Judaism, so Jews were hated for their religion,, then when race theories took off in popularity ( race theory was popular and respectable amongst many in the intelligentsia) Jews were hated for their race ( anti-semitism was coined by an advocate of this race theory movement to mark himself as progressive as he did not hate Jews for their religion but for their race), now that political theories of the progressive left are popular, that is the form modern jew hatred takes, as the Jewish nation ( and all Jews by extension as we have seen in all the terrorism and harassment of a diaspora Jews) are hated for allegedly ‘transgressing’ the values of the progressive left, as I outlined above.
It’s really undeniable that antiZionism is the modern Jew hatred, there has been a direct ctrl-alt-select all word replacement of Jew for Zionist in the rhetoric and language. We’ve gone from ‘dirty jew’ to ‘dirty Zionist’ , ‘Jewish scum’ to ‘Zionist scum’, Jews control the media to Zionists control the media, Jews control governments to Zionists control governments. Jews kill babies to Zionists kill babies ( in no other war have I seen this narrative against one side, still less the side that the war was started against).
So the question is not why Gaza? it’s ’Why Israel/ why antiZionism? and this is the answer.