Because it's technology?
The iPhone is a premium phone and you pay a premium price for it. Some would even call it a "luxury phone" when they compare it to other new Androids in the market. People buy it for the streamlined user interface and efficiency of its exterior design.
Even if we look at car sales most data show that people are more interested in midrange cars. The Volkswagen group owns Bugatti and Lamborghini but most of the sales come from small Volkswagen cars. The f150 is the best selling truck in the US and most of its sales come from the XLT model (midrange).
Sony said that 1 in 5 of every PS4 sold is a Pro. Steam also has 120m active users but most of them don't own the top of the line PC hardware in the market. You might get the occasional special edition console for a bigger price than the regual hardware but the only luxury/premium (whatever you want to call it) that will stay on shelves all year round are the Pro/X1X because most customers are interested in paying extra for the hardware not a special edition with a picture on it.
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