Because it’s a place where refugees stay. Those are called refugee camps.
Don’t like the name? Take it up with the UNHCR (which runs a few camps that are almost as old as the UNRWA ones, and just as permanent and citified (although vernacular one-story buildings, not tenements, because they’re mostly built in shitty locations not wanting for land).
Nobody regularly questions the refugee status of the Eritreans in Shagarab, the Sahrawi in the Tindouf camps or the Karen in Mae La, though.
Hey, one Right of Return per customer, and it looks like you already used yours…
I’ve just given you the names of several places and groups where those very much are the rules on the ground. There are lots more. They may not be as unapologetically open about it as UNWRA, but UNHCR maintains lots of refugees in that exact same 3rd and 4th generation limbo.
Israel can lift its economy-strangling blockades and stop stealing fertile land and water from the WB any time it wants to.