Sorry to say so, but that website is bullshit.
I calculated all my game's prices and it's approximately €170 not €120 lol...
It all depends when and where u bought it. And it also calculates it current value.
Never the less a website could never be absolute accurate. Its just a funny thing to show off nothing else.
Also not that i will get like 3000 dollar for my steam account if i would sell it tbh.