current Maximoff pet theory
Everyone knows the retcon is stupid. So let’s explain it away!
Why cut the Maximoffs off from Krakoa? Because little Luna Maximoff knows when someone is being mind-controlled and shows possible signs of precognition. (I think that was just everyone forgetting what her powers are/how they work, but I’m willing to go with it.) Let her visit even once, and the jig is up.
This could’ve been solved by manipulating things so that Luna appears to be someone else’s daughter, but that would have caused (1) Pietro to immediately flip his shit, (2) Wanda to immediately flip her shit, and (3) Medusa to immediately flip her shit, and (4) a paternity test, which would have revealed the manipulation.
So, really, manipulating things so that Wanda and Pietro appear to not be Magneto’s kids was the easier way to keep Luna and her powers away from Krakoa.
Who’s doing the manipulating? Not Magneto. Xavier doesn’t have that kind of power on his own, but he has telepathy and zero qualms about using said telepathy to fuck with/up anybody he pleases. (War hero and king of a sovereign nation Namor. Magneto. His own students. Himself. Every woman he’s ever dated, apparently. And so on.)
So my current pet theory is that, in the original timeline, the retcon didn’t happen, Luna visited Aunt Lorna on Krakoa and said, “Hey, there’s mind control spores in everyone’s brains?!” and started fighting spores, alerted her dad and other heroes, and that was the end of Krakoa. It took like an hour.
Xavier and Moira hated that. Xavier and Moira put together a small team of mutants including someone with time travel powers, someone with heavy-duty reality-warping or manipulation powers, and someone to troubleshoot whatever fuckups the first two might cause, and then sent them back in time to prevent Luna Maximoff from ever visiting Krakoa. Thus, the retcon.