People will gladly spend hundreds of dollars on "fancy plates" (aka china) that sit on display in shelves. Thousands or tens of thousands of dollars could be paid for paint on canvas, just because the paint arrangement is unique, or the person that did the painting is well known. People pay 5 dollars for a cup of coffee at starbucks.
I think it's just important to realize that spending isn't always a strictly rational process. That said, there are definitely significant pieces of engineering that go into a keyboard. Here, the keyboard is fully programmable and you can flash the firmware. For some people's workflows, this might be very important. No keyboard in your price range will allow that. This keyboard is equipped with a low-power ARM cortex, which means it can handle additional logic a typical keyboard can't. You can use "layers" and swap between them at a hardware instead of a software level. This means you can take your keybindings with you as opposed to needing to change the OS settings when you switch computers while using the same keyboard. If you have actual wrist issues due to an injury, frankly I would pay even more money than this to ensure that I can type pain-free or that the symptoms don't deteriorate. As someone that's worked in hardware, I can say first-hand that the plastic injection molds are extremely expensive for products not sold at a massive scale.
I could go on. I'm not a "keyboard collector" or anything, but I do have a keyboard that cost me over 100 dollars, and having used it for eight years now, I consider the price entirely reasonable given the utility its afforded me, and the longevity. Not to mention that I can replace keycaps if needed, I can replace the cord, I can reprogram it as my needs change, etc.
I can understand if English isn't your first language, that's not a problem. Tone-wise, I think if you genuinely are curious about something, just make that clear. Otherwise, the question comes off as a rhetorical one, where you're "asking" in the sense of "why anyone would be so stupid as to spend this much money is beyond me."