I think mainly a combination between: Planned scarcity and downfall due to their own marketing.
The latter is above all, they hyped the 3000 series as if it were really the greatest gift since the beginning of the earth, these were the cards that made life different, had the answers to all the questions and had some computing power left. To some extent they have lived up to their hype, but so is the demand. And that demand may be much greater than expected.
Planned scarcity is also an option. If you make a product exclusive, more people will buy it. This is possible with the price (such as Apple, which keeps its prices high so that the products appear more premium) but also with scarcity. If it is not for sale anywhere, it must be a very good card.
One last option might be that they just can’t make as many cards at the level they need, and they have taken the gamble that the new AMD cards would be worse. Then Nvidia simply remains the best, and they can use that as an excuse. However, it turns out that AMD could be catching up well, but let’s wait for the reviews for that.
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