Hearthstone has a soft currency called dust. Dust is used to purchase a desired card from Blizzard. Common cards cost 40 dust, legendary 1600. Dust is obtained from trashing cards: 5 for common cards, 400 for legendary. Players who want a specific legendary card are very unlikely to find it in a card pack. But they can trash the cards in the card pack for dust, and use that dust to buy it.
Blizzard gave a special name to purchasing with dust and trashing cards for dust: crafting and disenchanting. Yet this mechanic is far from the crafting we are used to in RPGs: no additional material is required beside dust, and all cards follow the same recipe. Rarity only increases cost. So why calling it crafting/disenchanting, and not buying/trashing? Why make a fancy UI, pretending that players are actually creating a card themselves, and not buying it from the store? I think it was so that players perceive dust as a regular game element, and not a currency. That way, players don't feel like they are purchasing dust (through card packs) with real money at all.
Blizzard actually introduced direct-purchasing (aka crafting) as a solution to what they say is a common trading-card game issue: when players obtain a rare card, they want to keep it, and they'll never trade it with other players. But that rationale is flawed. People who buy card packs will sell their duplicates if the game provides them an auction house. Blizzard probbaly did not want to go that route after their Diablo 3 auction house was overrun by gold farmers.