You've mentioned one of them, but I'm not sure that it was the most important one. On the question of enforcement, enforcement requires cooperation. You cannot enforce unilaterally. If the United States stays away from this treaty, says goodbye to it, what kind of enforcement provisions and what kind of enforcement leverage are we going to have. Let's say the treaty comes into force.
Someone violates it.
The treaty allows for flexible enforcement arrangements, a wide variety, depending on what the states agree upon. In the case of Iraq after the Persian Gulf war, there was enforcement because there was a common agreement about the dangers of Iraq's behavior and the dangers of their continuing programs. Circumstances in which you can do collective enforcement, outside of treaties, are extremely rare. It's much easier to do it inside a treaty itself. Anybody who cheats is not going to cooperate.