You said cores, not threads. In any case, 2 cores are still a thing. Even the new Macbook Air has 2 cores, so yeah...
Further, no one targets 16 GB RAM for a game. Not even the non-released, next-gen consoles have 16 GB dedicated CPU memory.
Similarly, not everyone one has an SSD and therefore companies cannot target that. Only in a few months with the new gen of consoles we will see actual games targeting SSD speeds.
Yes I made a mistake during editing the comment, I had processor threads in there before and somehow got mixed up with cores, my apologies.
As with the other points though, a low-mid tier gaming PC is something like 4 core/8 thread, 16GB ram, a HDD for bulk storage and an SSD for system & some select game(s). Someone that is buying a Macbook Air or an Ultrabook or something with only 2 cores is selecting it for something else rather than gaming. So irrelevant to the discussion.
The reason no big publisher targets 16GB for a game is because of these old consoles. The games can and do use more memory if available but they are limited by having to target these low spec consoles. They're also required to support the slow HDD speed of the current generation of consoles, so no exploiting SSDs either. This takes significant time and resources to optimise for!
Yes it's more of a mid tier system but it's a low end system that you would get to play games on.
Also given that games still target the consoles you can get away with 8GB of ram easy.