There are a lot of factors that go into one's decision to purchase luxury items. Not all of them are rational.
Look at the diamond industry. Diamonds are not rare in nature. But thanks to cartels who control prices and a culture that has been convinced that diamonds are highly desireable, you have people paying orders of magnitude more than the stones would otherwise be worth. Look at all the marketing that is going into trying to make "chocolate diamonds" the latest must-have variety. Those ads don't want you to know that brown diamonds are the most common and least valuable of all of them, but you throw on the word "chocolate" and make them sound prestigious somehow, and the largely uninformed masses will get sucked right in.
The comparison between artisan keycaps and jewelry (or gemstones) is a pretty good one. I'm not into either, but lots of people are. They want this stuff, for whatever reason, and there are manufacturers ready to cater to the demand. When it comes to such things, the cost to produce rarely bears any relationship to what buyers are willing to pay, because how much one is willing to pay is only really governed by how badly one wants it.
The reasons why people want such things, and in some cases want them badly, are many and varied and can't necessarily be explained logically.
