Your question piqued my curiosity.

I thought maybe NERSC doesn't accept jobs from private corporations but I checked and that's not true, as long as results are not held proprietary.

Perhaps ANL was used as they have a lot of compute and they lead and host the Genesis Open Models Initiative?

From your link, 2048 B300 GPUs were used for 6 months. If google search is right, NERSC has 7168 A100. B300's are way more capable than A100. To do this training in 6 months, "3 NERSCs" would be needed.

Between the political angle and the technical, I'd guess these two make up a big chunk of the answer.