Three reasons!
One, it is a very well known game.
Two, it is a pretty good looking game which is well optimized.
Three, it is locked to 60 fps! That gives us a tangible goal when building, and if we can meet that FPS goal you get the same experience as someone with a $3,000 gaming computer. Of course not all settings are maxed out, but it is running at 1080p.
Oh yeah, I meant for those to be a list. It should read:
Computer - $40
GPU - $120
SSD - $40
I don’t think I can edit the OP, sorry