Why was the First Triumvirate not an official Roman government office?

The "First Triumvirate," consisting of Pompey the Great, Julius Caesar, and Marcus Licinius Crassus, was not an official Roman government office because it was never a legally created commission or institution. Instead, it was an extralegal, private compact—often kept secret at its inception—formed by three powerful political leaders to advance their personal interests and secure mutual political goals.12

While the term "triumvirate" was used in Roman history to describe various official boards of three men (such as those appointed for land distribution or the later, legally sanctioned Second Triumvirate), the alliance between Pompey, Caesar, and Crassus was merely a convenient, modern label for an informal partnership. Because it lacked state authorization, it held no formal legal standing within the Roman Republic's constitutional framework.312