Typically they don’t really try to be attractive upgrades to owners of the previous generation. If you owned a 970, the 1070 wasn’t particularly sexy either. Good performance gain, but nothing earthshattering. But if you were rocking a 770, it was amazing.
The 20-series at launch was unique in that it offered essentially the same performance as the previous generation, no real improvement at all, and cost more. That’s why the 2070, 2080, and 2080ti are all terrible products.
But then Nvidia made a course correction. The 2060 performs like a 1070ti, but it costs less than any 1070ti you could ever buy, so it’s actually a decent deal.
And the 1660 runs like a 1070 but costs dramatically less than even the most heavily-discounted (new) 1070, making it a downright great deal. The 1660 is what we used to expect from a new generation. It’s what the 2060 should have been.