Do not overlook tour logistics. I guess it might not be viable to implement a tour somewhere if all parameters aren't met. Availability of venues on certain dates and many more things like that. Sorry for vagueness, but we don't know all variables that make up a tour, so...
I think Forostar is correct on never fading popularity in Europe. West and North Europe are Maiden's home ground too, since the early days. From there Maiden went to tour other continents and other European countries such as ones behind the Iron Curtain. While the popularity that Maiden built with Killers/TNOTB tours in America faded away by 1988, it never did in those "other" European countries. Nowadays being in some Balkan backwater might mean you have better chances of catching the best metal band nearby, than being in an U.S. megalopolis. That's called loyalty - rather opposite of financial greed - playing songs you wish to play for a loyal audience that pays $40 a ticket.