It's simply a question of hypocrisy for me , how can the country with the largest nuclear arsenal (America) possibly have the gall to say who can and cannot have nuclear weapons.
If I remember rightly Isreal refused to sign up to the treaty and yet they weren't forced to stay non-nuclear,, double standards from the US and UN I would say.

Israel - Israel is not a member of the Nuclear Non-Proliferation Treaty and refuses to officially confirm or deny having a nuclear arsenal, or to having developed nuclear weapons, or even to having a nuclear weapons program. Although Israel claims that the Negev Nuclear Research Center near Dimona is a "research reactor," no scientific reports based on work done there have ever been published. Extensive information about the program in Dimona was also disclosed by technician Mordechai Vanunu in 1986. Imagery analysts can identify weapon bunkers, mobile missile launchers, and launch sites in satellite photographs. It is believed to possess nuclear weapons by the International Atomic Energy Agency. Israel may have tested a nuclear weapon along with South Africa in 1979 (see Vela Incident). According to the Natural Resources Defense Council and the Federation of American Scientists, they may possess 300-400 weapons, a figure which would put them above the median in the declared list.