Anyone can tell me why someone want to pay 90 bucks for some fukken keycap?
You must be new here.
You'll soon learn most of us at GH are somewhat insane, and that $90 for a single keycap is by no means unheard of...
Yup my first purchase here was the cap in my profile pic for 70 USD. Some of the older and smaller run clacks have fetched upwards of $250.
The Titanium Skull was also my first keycap purchase. Think I paid $75 shipped for it from Feng...
Then there was my first CC, for which I paid (and resold for) $200.
Hey, I'm somewhat insane myself

Or I wouldn't be here.
Oh, and I collecting coins. Nothing very fancy so far, but...
And I think I understand. If it's a collector small-run item...