I did check about five brands of AMD graphics card on Newegg US before posting, and didn't see anything shorter than two years, with three and five years quite common. I also once bought an AMD card with a lifetime warranty, though I believe that particular manufacturer has since stopped offering those terms on any of their models.

So the question remains valid: what are the GPUs being sold with super short warranties, and are they even worth buying in the first place?

The situation was much different 5 or 10 years ago.

One year was the best you'd get, 90 days was common.