Because tarot is a symbolic language, and languages evolve to fit their speakers. The Rider-Waite-Smith deck (1910) used medieval European imagery because that was the symbolic vocabulary of its audience. A cyberpunk deck like Chaos Tarot uses digital and technological imagery because that's the symbolic vocabulary of its audience. The archetypes are the same; the costumes change.
Why Themes Work
The Tower is The Tower whether it's depicted as a medieval stone tower struck by lightning or a data center suffering a catastrophic cascade failure. The archetype — sudden structural collapse revealing hidden truth — is universal. But the imagery that makes that archetype immediately recognizable varies by culture and era.
A reader who works in tech will see the Chaos Tarot's "Network Crash" imagery and immediately feel The Tower's meaning in their bones. The same reader might find a medieval tower painting intellectually interesting but emotionally distant. Themes are bridges between universal archetypes and personal experience.
Choosing a Deck
Pick a deck whose imagery speaks to you without explanation. If you look at a card and something clicks before you check the meaning — that's your deck. The Rider-Waite-Smith is the reference standard (and most tarot books use it), but there's no requirement to start there. The best deck is the one you'll actually use.