I'm not sure. Maybe it was a limited edition? One of my first albums was Blink-182's live one from 2000, which according to the press-release was only sold for 2 months starting November 7. I got a copy in early December, and since then I haven't seen any other copy anywhere. Anyways, much later, when I visited Europe in 2011, I found some stores (I think Fnac in Madrid, and HMV in London) which still had copies.
Maybe
En Vivo! also had a limited release, so after the first pressing(s) of the album, there are no more copies - or, they will begin to surface at a later moment.
I'm also thinking that when The Beatles' (and Queen's, and Pink Floyd's, and Led Zeppelin's) latest remasters were released, the older (mostly '90s) CDs of those same albums almost immediately disappeared from the stores. I'm not sure, buy maybe that is a label decision - so the new CDs (which are way nicer but cost way more) don't have to compete with the old CDs (which were way cheaper in some cases).
Although in
Maiden England's case, the 'competitor' would be
En Vivo!, which represents a different tour from a different decade, so I'm not sure how that last theory would apply there.
Anyways: hey, I'm also a late-bloomer! In my teens I listened to some stuff (since a friend was a huge fan), but I was 22 the first time I decided to buy something. It was the
From Fear To Eternity compilation released in 2011. Some weak tracks there, but a good collection nontheless. After that, it was
En Vivo! and the last 4 studio albums.
I also gave a copy of
The Best of The Beast (and a few South Park DVDs) to my 10 year-old cousin. Boy am I a good influence