There are a number of reasons why (some of which I'll cover later), but at the core is this: they have plenty of individually powerful cards, along with powerful tribal bonuses
For even more guides on Pokmon TCG Pocket, be sure to check out our breakdown of the best decks to use
There are dozens of ways to draw cards from sacrificing creatures, and most of them are far, far better than paying 6 mana and skipping your draw step
Simple, immediately accessible, and tournament-playable, Young Pyromancer has seen play in every format where its legal
It's also so easy to get back to the battlefield that I think it ends up being pretty solid
Pull rate from Rare Packs: 2.63% The estimated pull rate for Espeon (Eevee Grove) from a Rare Pack is approximately 2.63%, meaning you might need to open around 39 Rare Packs to obtain it