I'm here for two reasons. One, Lyons needs me. He always has, just as much as I need him. We've been through a lot together, he and I. Two... Take a look around you. Access to this kind of technology, and the benefits it could provide to the Brotherhood, is immeasurable.
Scribe Rothchild was a member of Elder Lyons's exploration party when it discovered the Pentagon ruins. Rothchild fully believes in the Brotherhood of Steel and its ideals, but he is not a soldier. He's a scientist, and a good one. He is the Senior Scribe of the Citadel and takes his position very seriously. He is also thrilled that the months of bringing Liberty Prime online is yielding dividends.
Rothchild mentions a small detachment of Brotherhood in Chicago saying that they have fallen off the radar and gone rogue. The only known Brotherhood in and around Chicago is the Midwestern Brotherhood of Steel.
He might taunt the Lone Wanderer in repairing his/her gear, as asking him will yield the answer, "Could I? Yes. Will I? No. Ask Bowditch."