Racism.
You can see that by how American politicians go on and on about Israel being a "Jewish Nation", a characteristic that is wholly unimportant unless ones is a racist.
Since WWII and what was done to millions of Jewish people because of their etnicity (and not only them: there is this "strange" forgetfulness that for example people were also being exterminated for having the Roma etnicity) by the German racists that, even though the racism itself never died, Jews became "one of us" for the racists in many countries with a predominant white majority (in other words, they're considered just another kind of "white").
Israel itself seems to have invested a lot into portraying itself as a "Western Nation" to further entrench and capitalize on that "one of us" perception in Western nations,
Palestinians, on the other hand are seen by the racists as "muslims" and as some call it "brown people", with quite a lot of nasty prejudices associated with both characteristics.
For the racists this is an "people like us" vs "them" fight, hence why even very overt and extreme racist statement of the Israelis like calling Palestinians "human animals" don't shock them (they're pretty much aligned with the racists' prejudices about "muslims" and "non-whites") and hence too the vastly different reaction from how the invasion of Ukraine by Russia was seen, since that one from a racist point of view was "people like us" vs "people like us".
This, by the way, also explains Germany's behaviour on this: the Nazis might have been kicked out of power there but that very "special" way of looking at other human beings as primarily members of an etnicity and "like us" or "not like us" has never left, so Israel gets unwavering support no matter what and that's very overtly stated as because "they're the Jewish Nation" (notice how it's people etnicity that determines if support is given).