No, the primary reason given for rejection is that the term is merely descriptive—GPT just refers to a transformer that was trained with generative pre-training. The examining attorney gave a bunch of examples of GPT being used to describe a type of AI system.

So it's not that the trademark has been diluted (although the attorney included a warning that even if the trademarks weren't descriptive it's also become generic), the problem is that it would never have been an acceptable trademark because trademark law doesn't allow you to trademark a description of a product that would apply equally well to your competitors' products.