Soundwave on 01 October 2015
People were tired of the super long PS3/XB360 cycle and wanted a new system to upgrade to.
Sony made better design choices with the PS4 and thus had better early momentum than the XBox One which was crippled by the expensive Kinect 2.0.
And once the PS4 became the "go to" console, more people started to buy it because their friends had one and you want to be able to play with your friends online. So it all snowballs from there.
