It's about the joy of discovery, the thrill of finding rare cards, and the satisfaction of completing a set
5% market price cash, 10% market price in store credit, and they sell them at 500% market price.
The answer probably revolves around how many were talking about
Not only does this give you more play options by allowing more to happen at instant speed (upgrading Mantle of Webs to Sudden Spinnerets, for example), it lets you customize creatures like Grimdancer and Helica Glider to your needs by choosing their abilities as they enter the battlefield
Discard a bunch of Mad Party Pokmon with Ultra Ball or other discard engines, then move a Ditto to the active position for a surprise attack
As more people catch on, these trading card games are getting cleared from their shelves