system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are graphic cards so expensive? And why do AMD and Nvidia not have much competition?

Why are there no 'Chinese' knock-offs for graphic cards? If there was more competition, the big two (AMD and Nvidia) would have to reduce their prices. If there are so many Chinese phones on the market that do reasonably well, why not for graphic cards? After all, it's just hardware, just like in phones.
gpt
The key to a graphics card is the graphics chip (the GPU), and as you rightly note, there are only a couple of major players for graphics cards.  (Intel is also a major player for integrated graphics chips to go onto PC motherboards.) These chips are very difficult to design and make, and the 2 big companies are rapidly innovating, so even if someone put the millions of dollars it would take into reverse engineering and manufacturing one of their current offerings, they would already be old technology by the time they came out.  There are a lot of companies that make cards using Nvidia and AMD/ATI chips, but they still have to buy the relatively pricey GPUs and graphics memory chips to put on them.   
  
These cards aren't sold with an extremely high profit margin, and they are already built in cheap factories in Asia. The only way for a knock-off to be a lot cheaper would be to make their own graphics chips. Nvidia and AMD/ATI put a lot of money into developing these chips, so doing it from scratch would be very difficult (if you wanted to make a competitive product). The "big 2" also get their chips made at very competitive prices, since their volumes are large enough to give them very strong negotiating power with waferfabs.  
  
A knock-off company would also face obstacles getting their parts built. TSMC and Global Foundries don't want to anger customers who are among their largest, so once a "knock-off company" was found out, they'd probably discover that the waferfabs would refuse to make their chips any more, and they'd be out of business.  
  
Why are they so expensive? GPUs are very big chips, and that makes them much more expensive to make. When you double the size of a chip, the cost of the chip goes up more than 2x. That's because the probability of getting a defect increases exponentially with chip size, rather than linearly. And if a chip has even one defect in the wrong spot, it has to be discarded or sold as a lower functionality chip. (Some defects can be "repaired", if they affect memory arrays.)  
  
With that said, it would be possible to compete with AMD/ATI and Nvidia. You just have to design and build a better product than they do.  But they have had a lot of learning over many generations of chips, and they're pretty good at making them. Intel has tried for years to beat them and has not succeeded (in the high-end market).