Why 90% of Arabs who say they are "native palestinians" were born out of Palestine?

I understand your confusion and all the false information that you provided my dear friend. It must be because you are from Israel where you received the kind of education that is different than the one we have in normal countries. So to educate yourself more, read Ottoman and British official doents and reports - the Survey of Palestine, Justin McCarthy, Yehoshua Porath, ...etc - and as well all the genetic studies that prove the Palestinian Arab ancestral origin in Palestine.