I'd say the popularity of the 6700K has a lot to do with its price point. Paired with a GTX 1070 or RX 480, for around $1000 you can build a very good gaming PC

I'd say the popularity of the 6700K has a lot to do with its price point. Paired with a GTX 1070 or RX 480, for around $1000 you can build a very good gaming PC. If you want 6 cores you can get a 6800k for $150 more, but it also has a higher TDP and requires a more expensive motherboard (X99 vs Z170 chipset). This is going to put the total price up by at least $300. As you say most games still favour single-core performance so paying extra isn't worth it. DX12 and Vulkan will start to change that though, so let's see...