Primarily, thought not exclusively, becuase of these verses:

1 Timothy 3:2-7:

Therefore an overseer[a] must be above reproach, the husband of one wife,[b] sober-minded, self-controlled, respectable, hospitable, able to teach, 3 not a drunkard, not violent but gentle, not quarrelsome, not a lover of money. 4 He must manage his own household well, with all dignity keeping his children submissive, 5 for if someone does not know how to manage his own household, how will he care for God's church? 6 He must not be a recent convert, or he may become puffed up with conceit and fall into the condemnation of the devil. 7 Moreover, he must be well thought of by outsiders, so that he may not fall into disgrace, into a snare of the devil.

Because if you let women have authority, people might start believing things like "men are not automatically good without needing to actually do good things" and "authority isn't instantly derived from the circumstances of your birth but instead based on your merits as a leader".