TJ Hooker :
A GTX 1060 6GB is already a fully enabled GP106 chip. I guess the yields for the GP104 GPU were good enough they didn't feel the need to offer a version cut down further than the 1070. Maybe they felt the losses from potentially cannibalizing their 1070 sales with a 1060 Ti would be more than what they would lose from not having a product between the 1060 and 1070. Especially because AMD doesn't have anything between those price points either.
I agree with what was said above, they should have called the 1060 6GB the Ti to reduce confusion between the 3 and 6GB versions of the 1060.
to bad the 1060 6gb was announced first, if the 3gb was announced first, for sure, NVidia would call it 1066 the 1060 ti and milk the consumer.