While having each deck correspond to a single game is thematically tight, it doesnt make the best use of each Commanders strengths
It also forms a well-known combo with Dramatic Reversal to generate infinite colored mana when you have enough nonland mana sources, giving cantrip-heavy lists and spellslinger commanders an easy way to close out the game
(Source) Oh, Pikachu Illustrator card, where do we begin
Having access to your best spell whenever you want it, and getting a body as well, allows you to close out the game incidentally, as a side-effect of cementing your control over the game
It's just built into the price because we think shipping charges on a premium product are unnecessary friction
When Asmoranomardicadaistinaculdacar enters the battlefield, you may search your library for a card named The Underworld Cookbook, reveal it, put it into your hand, then shuffle