There are two reasons why. Firstly those living there already can decide to be good citizens of Israel or if not happy THEN they can leave. Secondly , every country needs a variety of peoples. Allowing the country to be solely Jewish is stupid because it would breed radicals who will come out of the "woodwork" to make other Jews be they conservative, orthodox , or secular bow down to strict religious dictates.
Northern California wildfire doubles in size, displaces thousands (Reuters)
from the article: Ministers support bill annexing Jordan Valley settlements to Israel