Perhaps that Sonic lore never seems to be absolute. There are core events that happened but even they can be twisted and moulded to suit the current status. Shadows origin for example, Maria is a certainty but Black Arms...maybe? Sonic, the protagonist, has even less history. It's an ever changing world, and it's probably why people love to make AUs for it. You have a baseline to work from and...like Sonic....you can run wild with it. Aliens, magic, time travel, mystical ruins, human interaction, end of the world, ancient Kingdoms. It's all there