"I have never understood what purpose Israel has in maintaining the silence about its nuclear arsenal." I am not sure about the claimed reasons at the moment. But very often these things build up inertia, and people make up reasons to continue the status quo rather than consider any change. Originally, when Israel had a nuclear program the USA was concerned that they might be making nuclear weapons, and Ben Gurion promised that the program was for entirely peaceful purposes. (It seems that he felt Israeli nuclear bombs were peaceful because he didn't intend to drop them on anybody but to prevent wars by threatening to use them.) And Ben Gurion promised that Israel would not be the first to introduce nuclear weapons to the middle east. Kind of like, "OK, everybody knows they're here, but we haven't broken the promise until we *introduce* them." All very diplomatic.
Ya'alon okays administrative detention of Jewish extremist suspected in church arson (Haaretz)
from the article: Israel missing a chance at nuclear global legitimacy