Well, because it essentially doubles as a reanimation spell at instant speed
Not only does it increase your consistency for curving better than basically any other red card but it also lets you build with more risks
This is one of the cooler cards, with a token-style deck possible with it
The popularity of the Storm Scale then led to a host of other scales: The Rabiah Scale The likelihood of a plane returning The Venser Scale The likelihood of a Planeswalker returning The Beeble Scale The likelihood of a creature type returning The Gotcha Scale The likelihood of an acorn mechanic returning This led me to writing eight different Storm Scale articles: Khans of Tarkir block Ravnica and Return to Ravnica blocks Zendikar and Battle for Zendikar blocks Innistrad and Shadows over Innistrad blocks Mirrodin and Scars of Mirrodin blocks Kaladesh and Amonkhet blocks Theros block and Theros Beyond Death Throne of Eldraine through Strixhaven : School of Mages I've also written three articles on the Rabiah Scale (Part 1, Part 2, and Part 3)
For already-invested Warhammer players, this was a fun way to include major lore moments they were already familiar with and also a tool to teach them how mechanics can have flavor
In fact, it can theoretically churn out more than 6 mana on turn 4, which allows you to cast heavy hitters faster than your opponent can react