The Non-Proliferation Treaty (NPT) was negotiated with the expectation that future progress on nuclear disarmament would be necessary to ensure the treaty's sustainability.
The security benefits of the NPT meant that states were not willing to make the non-proliferation obligation conditional on the achievement of specific disarmament measures, which explains the vague language of Article VI. This calculation likely remains true today.
Anxiety about disarmament during the NPT's negotiation was fundamentally a matter of politics, and was not confined to non-aligned states. This also appears to be true today.
The NPT review process was partly designed to encourage states to debate progress on nuclear disarmament, but review conferences lack the ability to resolve those debates.
Some states that pressed hard for disarmament concessions in the NPT negotiations also harboured nuclear weapons aspirations; today, disarmament advocacy can sometimes provide political cover for those seeking to undermine non-proliferation. However, the perceived injustice of the NPT bargain is acute, and ‘calling the bluff’ of non-nuclear weapons states dissatisfied with progress on disarmament risks generating political momentum that can also damage the treaty.