When a starship is launched, there are a huge number of hoops for it to jump through to be cleared for launch- to be allowed to come even close to seeing the light of day.
Then one ship that came up short of all those hoops was granted an exception because of how unique it was- there likely wasn't any set of hoops it could hop through, simply because it wouldn't fit. It was too large.
Unfortunately, while it launched successfully, its builder- and owner- was already dead.
So, with nobody left with a claim to it, it fell into the ownership of the Navy- under whose authority it launched. And what is the Navy going to do with a starliner of this size?
Personnel movements, of course! If anyone wants a ride to fringe worlds at the warfront, or back from them, and doesn't mind becoming a cute magical pony for the rest of their lives, she can get them home and back three times over in the same time that even the fastest other ship would require just to get them home the first time.
Updates on Thursdays, when ready. Why didn't I have this note in here before...?