Historic stuff.
Palestine was a country, or a region/territory administrated by the British. The formation of Israel was a bit of a historic coincidence, the empire was beaten by WW2 and scoping down and giving independence because the colonial stuff couldn't be maintained any longer.
The situation with the europen jews was problematic, because even though Nazi Germany was defeated, the prejudices against jews weren't removed by snapping your fingers and the question of where the millions of victims should go and live was open. Putting them into Palestine and creating Israel was a convenient alignment of both the political opportunity and the public opinion of people who wanted the jews gone and the jews who wanted to leave and live in Israel instead.
You may notice that the one group that wasn't asked in this situation was the population of Palestine.
That's sort of the short version of how Israel came to be.
The situation with the Kurds is completely different. They have no real external political support. The countries where "Kurdistan" would be "belongs" to intact, functioning sovereign nations, who all between each other agree to the current borders. And who all can field the military and governmental power to enforce that claim, both externally, but also internally. Because of how international territorial disputes are resolved, this is a "solved problem" diplomatically and internationally.
Kurds who are pro Kurdistan and... well, armed, are treated as rebels against the government. And other governments also don't like rebels in their countries, so the question of how legitimate the claim is, doesn't even get debated on that level.
So in short, supporting a "free Kurdistan" looks more like support rebels and terrorists, compared to palestinians who drew the short stick in a historical conflict and who are an underdog and "legitimately defending" themselves. So associating one-self with that is easier than with Kurdistan.
(And I'm not judging the legitimacy of any party in any of the conflicts, everyone has their story.)