How did they become such a valuable commodity
Currently, it is being added to many Chatterfang, Squirrel General lists
(1) During either players turn: You can add 1 monster that mentions Ritual of Light and Darkness from your Deck to your hand, then discard 1 card
Espathra ex 214/91 Loading
Spells with this kind of effect are becoming increasingly problematic in Magic - if seven mana additional turn spells like Nexus of Fate and Alrund's Epiphany can get banned, it's easy to see why Time Walk is so scary
For example, if a Lakeside Shack and a Breeding Pool you control are entering at the same time (perhaps because of the effect of a spell like Scapeshift), your life total is 14, and your opponent's life total is 20, the Lakeside Shack will enter tapped whether or not you choose to pay life as Breeding Pool enters