Due to their departure, no one knew that the Isles were once the home of the Archfey. Though they departed, their touch still extended the lands. The vast amounts of leylines that encompass the isles ensured that there was always a way to power wards. While I couldn’t touch that for 12 Grimmauld Place, due to the existing system tied to the existence of a blood relative, I could for my home. Now that this would be a new ward system, they would be far more powerful and potent because of being powered by the leyline that runs beneath the ground. 