I seemed to remember reading that it was a record company driven decision - they wanted a "single" release to promote the album and the band didn't have anything ready having used up all their catalogue of songs on the album.
The original was done by a Australian rock band (the name of which I can't remember) and Maiden heard it , liked it, so recorded their own version of it.
Thats what I remember reading somewhere, mind you it was a few years back, so if I'm wrong please feel free to put me right!