This exactly.

There probably never was a "3080 12GB". It's likely it's always been a 3070 and Nvidia did this because they're scumbags and wanted to push people towards the 4090. It's all very coincidental that they make this decision after the launch and 2 days of buyers getting their share.

Edit:

Looks like AIBs actually have produced 4080 12GB cards as they're now deconstructing these, and I doubt they'd get in on a conspiracy with Nvidia. So Nvidia really do just like fucking everyone over.