This is just absolutely false, Steam says that 4.21% of users play at 4K. The number of users that play at higher than 1440p is only 10.61%. So you are wrong, simply wrong.
This is a chicken and egg thing, though - people don't play at 4K because it requires spending a lot of $$$ on top-of-the-line GPU, not because they don't want to.
Did I say all the people, or did I say many people?..
Why are you so hostile? I'm not justifying the cost, I'm simply in the 4k market and replying to OP's statement "Any modern card under $1000 is more than enough for graphics in virtually all games" which is objectively false if you're a 4k user.