I have to assume Killers has been on the shortlist for a few tours since 1999. It would've been an obvious choice for Eddie Rips Up the World, the Maiden England tour songs were primarily selected based on the video so Killers had to have been a consideration there, and it would've been a decent choice for LOTB as well. The band seems to enjoy playing it and it seems easy enough to put together, so I imagine there's just always been better choices for the given tour. Would love to see it make a return before they retire.