The Gold Mew card is a collectible because it is incredibly rare. Only 6 of them have ever been released, and they can be extremely hard to find. This rarity makes them highly sought after, and this drives up the price drastically. Collectors place a great value on these cards because of their limited availability and the fact that it was part of an important set in the trading card game industry. The Gold Mew card also holds a special place in the hearts of many Pokemon fans, who appreciate its unique design and heritage.