I don't understand

It's just your steam-level. Which you can basically push with money or time (a bit at least). It has no real inherent benefits beyond a certain level. It's to show off basically. For me it was the thrill of finding the most efficient automated method to gain it as fast as possible. A silly idea in hindsight, but I can get pretty obsessive 😑

Also how big is your steam library

Too big. And while it might sound much, it's over a course of over a decade. And I buy whatever comes out and is adjacent to my likings. So my backlog is too vast to manage in this lifetime. Nowadays I buy much less. Either to support indie devs or those I REALLY wanna play.

And where I live, this money wouldn't buy you a house. Not even an apartment. Except you don't mind burned down houses or so 😁