そもそもホワイトハウスの発表ではこう書いてある

https://www.whitehouse.gov/briefing-room/statements-releases/2021/05/21/u-s-rok-leaders-joint-statement/

The two sides reaffirm that close coordination on all matters related to global nonproliferation and safe, secure, and safeguarded uses of nuclear technology remain key characteristics of the alliance, and the United States recognizes the ROK’s global role in promoting nonproliferation efforts. Following consultations with the United States, the ROK announces the termination of its Revised Missile Guidelines, and the Presidents acknowledged the decision.

核兵器拡散防止協力に対する韓国の努力を認めて改定ミサイル指針を終止させると言ってるから
弾道ミサイル開発したら共同宣言違反になるから無理