Steam knows exactly how many hours went into every game somebody owns, and shows it as a list sorted by a number. A list is the one shape that cannot answer the question people actually have about their own library, which is not "what is on top" but "what did all of it add up to".
So this site draws the library to scale instead: one rectangle per game, area proportional to hours. Thirteen years of a Steam account become one picture.
The rest of it grew out of that. Every game that was ever launched gets a page built out of that game’s own interface, because a shared template would have made a hundred and fifty-nine different games look like one spreadsheet.