While each of them are mono-colored, they come with Kicker costs in the two other colors in the wedge and you can choose to pay both of them, and when you do you end up with quite the formidable creature
The enchantment certainly offers a lot of utility in the right deck, but considering how narrow it appears at first glance, its rather shocking to see the card this popular
Im also really excited to see people kill themselves with it
And theres a load of interesting cards
Thirst for Knowledge, and more recently Thirst for Meaning, have offered this card selection at instant speed for years, but its so much easier to have an abundance of expendable basic lands in a deck than artifacts or enchantments
When the first buyers, driven by a powerful fear of missing out, pay that price, it validates the high cost and creates a feedback loop