To be effective, multilateral regimes need to get three things right. They first have to ensure levels of participation adequate to solving the problem at hand. They then need to require adequate action from all parties. And finally have to encourage, or enforce, compliance.
Participation. Action. Compliance. Achieving only two of these three objectives is not enough.
Without adequate participation, encouraging action and compliance is meaningless. Consider a non-proliferation treaty where even one of the proliferators is left out: this would lead at best to non- compliance and at worst to a collapse of the regime itself.
Similarly, without compliance, achieving adequate participation and requiring action would lead to underachieving on the objectives, and alienate complying parties: a fisheries regime where the quotas are constantly overshot would lead to a collapse of fish stocks and of trust between parties.
And without adequate action, compliance and participation become meaningless. If the prescribed reduction in total warheads is not sufficient to reduce the dangers of proliferation, then whether or not parties comply does not matter. Equally, there is no point in agreeing to fishing quotas whose limits are largely beyond what is required necessary to preserve the stocks.