system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do game makers know what computer specs you'd need to run the game?

My guess is that they use different PCs and make the game at different quality but that'd take too long so idk.
gpt
Games undergo an optimization process to ensure they operate reasonably well on a reasonably inexpensive machines. This involves improvements to the code of the game to make it run more efficiently and avoid unnecessary operations, as well as providing the lower-quality textures and various filters that make up the "video settings" menu in the game. 

During this process they typically target a few different common specs that they want to support well - for example, many games are optimized to use about 3GB of VRAM at their highest 1080p settings, since the GTX 780 is an extremely popular card among 1080p gamers (while 4GB and more is usually necessary for 1440p or 4k.) Of course, it is also important to provide a good experience for everybody using a GTX 680, 770, or one of the various R9 AMD cards with 2GB VRAM.

CPU performance is pretty linear - it's not difficult to ensure the game runs on an i7, i5, FX-8XXX, and FX-6XXX and figure out at what point the game stops working. Most games are optimized to run on 8GB of RAM.