>>41942965It would depend on which series you're set in. If you're talking GX which is a few decades after the game was introduced, then yeah there wouldn't be that much in terms of cardpool. For reference Yugioh just recently surpassed 10000 cards.
But other series span centuries into the future, spanning multiple countries, worlds, and even alternate dimensions. In those series there would be potentially infinite number of cards.
Remember this is the BIGGEST THING EVER we're talking about. The entire universe revolves around Duel Monsters, nothing else matters.