Because you are probably spending 3K in 3 months anyway. If you absolutely aren't (or you can't hit the minimum spend in other ways [pay for your friends etc.]), sure, don't get the card.
One card with a yearly fee is probably worth it for the other benefits. Other than that, the traditional way is to downgrade it to a free card. Either way, it's fine if you think it doesn't make sense for you, but it's pretty much no-hidden-costs net positive, and that's why so many people actively churn.