Why doesnt Hamas declare an independent Gaza state ?

Gaza is Part of Palestine. It is an indivisible unit.
Of the 2 million Palestinians living in Gaza, 70% of them are refugees who were ethnically cleansed by Zionists from their lands and properties in neighboring Palestinian cities, and villages.
Why doesn’t any city in the world declare their city as a state separated from their family and relatives in other cities in the same country?
Why doesn’t Zionists declare Tel Aviv built on Yaffa in Palestine a state, and give the rest back to Palestinians?
Divide and conquer tactics will not work.