Another reasoning, why don't they put vertical stabilizer on the center of the plane like a normal human being? Vertical stabilizer out at wing's tip have one advantage, they don't get obscured by fuselage at large AoA, re-entry vehicle typically does that, check NASA X-38, russian Klipper design is similar in that regard.
One more point for my sub-orbital theory.
One more point for my sub-orbital theory.