Because of the title...that's literally what it means. It's a function of the office of Deacon. That's why she was in Rome. She was there to teach as she was trained by Paul and sent with the letter. They were supposed to treat her the same as they would Paul. She knew the contents of the letter and she was to not only read it but teach the contents more thoroughly...to the church elders in Rome.
While a deacon who operates in their position obtains great boldness in their ability to evangelize, the role itself is not traidtionally one where a deaconness is given the opportunity to teach or usurp authority over a man. If a deaconness is given an opportunity to teach a man, there is always a man over her as a covering (as was the case with Priscilla and Aquila) who can correct her in the case that she might be deceived on something.
Because, I will say again that I believe that women are more spiritually inclined and are therefore more inclined to accept a doctrine because it seems spiritually viable and appeals to the emotions.
Whereas men are more analytical and would be more inclined to examine the scriptures carefully on any given subject to make sure that they will be preaching sound doctrine in any teaching situation.
1Ti 2:13, For Adam was first formed, then Eve.
1Ti 2:14, And Adam was not deceived, but the woman being deceived was in the transgression.