The fact that this combo is pulled off by the interaction between a lotus artifact (which are very prominent in East Asian and Japanese Buddhist art and symbology), a moonfolk from Kamigawa (a plane directly based on Japan), and the legendary creature that represents the patron spirit of all moonfolk
Shiny Pokmon, rare Pokmon that have an alternate color scheme, have been sought out by Pokmon fans ever since their introduction in Pokmon Silver and Gold
Pikachu Illustrator is extremely popular with collectors due to it being designed by Atsuko Nishida (Japan), who is credited as the original creator of Pikachu
The ladder format is the biggest reason why Ancient Tomb fetches a heavy price tag
As a card with a serious Legacy pedigree, it's always a piece or two away from becoming part of an extremely obnoxious combo
If your budget allows for 5-8 of them, chances are good that you'll get great use out of them, especially in a 3 or more color deck