I've kept them because they're important to me, and I think for at least some of the people who bid for these expensive cards, it's more about regaining a lost part of their childhood than it is about snagging a card they can hopefully sell in a few years for a profit
There are several reasons why the Pokemon TCG rotates out cards, but the three main ones are that it minimizes power creep , it keeps the meta fresh , and it helps The Pokemon Company to sell more cards
Its one of the few things he didnt grab. A disturbing pattern This is not an isolated incident
Your odds are 1/32 for one of these, making them relatively common as a side effect of the hunt for more valuable cards

Alpine Moon Anim Pakal, Thousandth Moon Arlinn, Embraced by the Moon Arlinn, the Moon's Fury Bad Moon Benediction of Moons Blood Moon Bound by Moonsilver Brinelin, the Moon Kraken Call of the Full Moon Chaos Moon Circle of the Moon Druid Cult of the Waxing Moon Day of the Moon Eztli of the Thousand Moons Full Moon's Rise Hallowed Moonlight Honeymoon Hearse Howling Moon Ichormoon Gauntlet Imprisoned in the Moon Kami of the Crescent Moon Kami of the Waning Moon Lace with Moonglove Magus of the Moon Mistmoon Griffin Moon Girl and Devil Dinosaur Moon Heron Moon Sprite Moon-Blessed Cleric Moon-Boy, Dino Rider Moon-Circuit Hacker Moon-Eating Dog Moon-Vigil Adherents Moonblade Shinobi Moonbow Illusionist Moonfolk Puzzlemaker Moonglove Changeling Moonglove Extract Moonglove Extractor Moonglove Winnower Moonhold Moonlace Moonlight Bargain Moonlight Geist Moonlight Hunt Moonlit Ambusher Moonlit Lamenter Moonlit Meditation Moonlit Scavengers Moonlit Strider Moonlit Wake Moonmist Moonrage Brute Moonrager's Slash Moonring Island Moonring Mirror Moonrise Cleric Moonrise Intruder Moonscarred Werewolf Moonshadow Moonshae Pixie Moonshae Pixie Moonshaker Cavalry Moonsilver Key Moonsilver Spear Moonsnare Prototype Moonsnare Specialist Moonstone Eulogist Moonstone Harbinger Moonstone, Harsh Mistress Moonveil Dragon

Current listings for this relatively rare card are sitting at about $140 USD