Well, because people deliberately use the naming to muddle things. Are you referring to 'Palestinian' in terms of geography, ethnic identity, political state?
Before 1948, 'Palestinian' was only a geographical term, and referred to everyone who lived in the region, whether Arab, Jewish or Christian.
Then Israel declared themselves a nation, and Jewish Palestinians took 'Israeli' as their identity as well as political nationality.
There was no Palestinian political state. Not before 1948. And not after 1948, because they chose not to. Because they wanted the whole land, and couldn't accept the 1/3 of the population who were Jewish having self-determination.
'Palestinian' still wasn't a particular Arab identity at that point either. Still just geographic.
Then in late 1960s, Arafat coined 'Palestinian' as a political identity for Arab Palestinians only - ie defined in opposition to the Israelis (who had been Jewish Palestinians until 1948). And started seeking a political state. But there had been enough war by then that Israel was no longer keen (had previously been fine with it, in 1948)
So it's a bit meaningless to call it 'Palestinian land'. The geographical term isn't linked to the new political identity. The geographical term applies to both Jewish Palestinians (who are now Israeli) and Arab Palestinians (who are now 'Palestinian', but have no state.. But are no more geographically Palestinian than Israelis are).
It would be like saying that 'Northern' land in the UK belongs to 'Northerners'.
But then saying that 'Northerners' excludes 'Geordies' from Newcastle...simply because they have their own identity (like 'Palestinians' seek to exclude Palestinian Jews, because they have a separate identity as Israeli)
And then stretching that to say that Newcastle is 'Northern land'. And 'Northern land' belongs to 'Northerners' (which we've now said excludes Geordies). So Geordies aren't allowed to live in Newcastle 