So, in my world, Terrans, also called humans, have colonized a hefty amount of Milky Way Territory, and have many subjects under their rule, about 200 billion spread across a space about 1,350 lightyears. Earth is the main capital of all human colonies in the galaxy,and the flag of the Terrans sports a phrase at the bottom in Latin, which says “Terra non fecit” or Earth will never die. Other main planets in the Terran territory are Amon, in the Alpha Centauri system,Tengelle, in the Orion system, and Kelstar, a system near where Tau Ceti is. Their are thousands of other, lesser known planets in between the main 4 like Torlon, Deloron, and the Orion Territory, but the 4 main planets all have something in common.
All the main 4 planets I mentioned above have one thing in common. Their all clustered near the edges of Terran space, even Earth, the Capital. It would make more since to have the planet in the uttermost center of Terran Territory be capital as it it closest to planets in the center. What would be a plausible reason why the Terrans would have their Capital be a planet far away from the center of their territory?