Price points and market
"However they seem to have forgotten to release an upgraded GPU in this cycle"
Why would they? That's not what they do :)
They have solid GPUs at the major price points. Sure, the consumer grade over 600 quid ePeen market hasn't got any offerings, but who cares?
If you've sold GPUs, you know there are roughly three tiers to what you sell. Entry level gaming 80-150 quid, all purpose GPU (gaming, media work) 230-300 quid and "high end" cards for 3-500 quid. Plus maybe something premium. But I would sell a couple of dozen 1060/570 grade cards for every 1070/580. And while it's not impossible to sell, a 1080 or Vega will sell once a month at most.
So consumer grade GPUs over 500 quid seem (to me at least) to be an extremely niche market.
Now data crunching GPUs are a different beast altogether. But they can cost 10x consumer grade and still be a rounding error in the budget for the tasks they are being used for. And AMD make some nice toys for that market, but you'll not see them on GPUBoss :D