Why do gamers use 60% keyboards?
The main reason gamers will use compact 60% keyboards is because the smaller form factor allows for more space for your gaming mouse. That means you can have to DPI levels in your mouse lower, offering greater accuracy but also necessitating wider sweeping movements.
It also means that your hands resting on the WSAD keys and the mouse are closer together, which in turn improves the ergonomic posture, either when gaming or simply using your computer.