Has it ever been explained why every single shield world we've encountered so far has been different from the last? One is a massive slipspace pocket inside a world made of sentinels seen nowhere else. One is a hollow planet with a terra formed interior and a fleet of warships. One is a metal shell surrounding a hollow planet/Promethean fortress. And then another is a metal shell that can break apart and reform into a shell or ring, that originally surrounded a planet. They're somewhat similar, but all are different. The most egregious seems to be Onyx, which is so vastly different in size and construction than any of the others...I just want to know why. And on that topic, has it been explained how the shield world in Halo Wars became host to a massive flood infection? And why the flood never escaped that planet, despite the presence of a gravemind and ships (albeit crashed ones) on the ground?