That makes them susceptible to artifact removal, but the reward outweighs the risk
You can get an artifact creature and an enchantment creature to accompany your target creature
The dream is to cast it for no mana and draw 6+ cards
The Necromancer
Heres a ready-made combo for you: get Babyhead, Jingle Joe, and the pterodactyl on the board
More than anything, these moments seem to be self-perpetuating, where everyone gets tremendously excited about one particular card, which creates demand, which raises the price, which exaggerates the rarity, which creates demand The next most expensive right now is the Latias ex at almost $200, then the gold card version of the Pikachu ex at $100, and that Hydreigon pictured above at about $95