I bought a theme deck (or a 2-Player Starter Set), and there are a lot of duplicate cards in it. Why is that?
The theme decks are for playing the game. So, there are plenty of copies of the cards you need to make the deck playable (like Energy cards). If you just want to collect Pokmon cards but don’t want to play (which we think would be a real shame because the game is really fun!), then you probably should buy booster packs.