If there’s one single thing that’s helped the band to last: it’s integrity. They’re honest with themselves and the fans, they stick to their guns, and they play the music they want to. Listen to a lot metal and hard rock from the 80s, and it sounds like it’s from the 80s. Iron Maiden transcended that by never bowing to trends and playing actual timeless music. There’s very few artists that do that, and most of them are now dead. Dio, Lemmy, Bowie, just to name a few.
I love me some Judas Priest, but their albums sound exactly like the year they came out.