The Moon administration was not in favor of the THAAD deployment and made things hard on USFK to sustain the unit such as delaying the environmental assessment:
A thorough investigation is necessary if there are suspicions that the previous Moon Jae-in administration deliberately dragged its feet in normalizing the U.S. THAAD missile defense system in South Korea, a senior presidential official said Wednesday.
Allegations have arisen that the Moon administration deliberately delayed the publishing of an environmental assessment report of the Terminal High Altitude Area Defense (THAAD) battery base, which was installed in Seongju, 214 kilometers southeast of Seoul, in 2017.
Since its installation, the unit has been kept in a temporary status pending the assessment.
“The normalization of the Seongju base is an essential measure for the Korea-U.S. combined defense posture,” the official said. “If there are suspicions this measure was deliberately delayed, I think we have to provide related facts to the people through a thorough investigation.”
Normalization of the THAAD base picked up speed after President Yoon Suk Yeol came into office.
Earlier this year, the environment ministry concluded that the base poses no health hazards, saying the maximum amount of electromagnetic waves emanating from the THAAD base was just 0.2 percent of the legal safety protection standard.
Yonhap
You can read more at the link, but the Yoon administration should also investigate why the Moon administration allowed protesters to almost continuously break the law and block the road forcing USFK to move personnel and equipment to the THAAD site via helicopter.