1. No one is forcing you to buy new video cards. Every new card released is an option: additional freedom of choice. Most people like having choices.
2. NVidia has a certain margin on each card. Even if every consumer on the planet abstains from buying, they won't produce cards below margin. And, if they don't receive that margin plus enough extra to cover R&D and a reasonable ROI, they will stop developing new and better cards entirely.
That's how economics work. You may not like the fact that many people find these cards an attractive price-for-benefit option, and enough of them do so to keep NVidia producing them-- but those consumers are financing the next wave of graphics. They are the solution, not the problem. There are hundreds of thousands of different industries in the world, and you would be hard pressed to name one that has advanced more and faster in the last decade than graphics cards. That's what these high prices give us ... and we all benefit from it.