This is because personnel of the Ministry of Defense, including the uniform team and the sebiro team, are considered as a part of Self-Defense Forces (Self-Defense Forces Act Chapter 2, Article 5), and the Self-Defense Forces are restricted by the political acts (in the same Act; Chapter 61, the same implementation orders; Article 86).
なぜなら、防衛省の職員は、制服組はもちろん背広組も自衛隊の隊員とされ（自衛隊法2条5項）、隊員は政治的行為が制限されているからである（同法61条、同施行令86条）。