To be fair, should all nations allow to own nuclear weapons?

For the same reason we do not hand a gun to a mental patient.

We don't go after Israel becuase they're as likely as NK to use them out of spite and unlike NK actually have allies to cover them. As for Pakistan... We like the Indians and don't want them turned into glow in the dark glass.

NK can't really nuke anyone as they haven't developed a system to deploy their nukes and their nominal ally China hates them as much as everyone else and only keeps them around to avoid having a pro-West Korea on their border.

NK can be punished without collateral damage, Isreal and Pakistan can't.