From the discord

The Raider Deck is like a battlepass, where you can spend Cred in order to unlock cosmetic rewards. There are a number of rewards to unlock per page in order to progress to the next page. The number of pages in each Raider Deck may vary. At launch, the Raider Decks will be free, but you can expect a mix of paid and free Raider Decks as new ones are added.

Raider decks are battle passes. The industry standard is that the one that comes with the game (or a paid expansion) is free while all others require money.

And there’s no reason to spend money if you don’t care about cosmetics, but most people do care and the cosmetics are way overpriced.