I'm surprised we haven't seen TPU cards (think Coral AI but at a larger scale) being made and sold for this purpose, especially if they're faster and more energy efficient at AI-oriented tasks than GPUs.
Well there is the asus AI Accelerator card but that's just 8 coral TPUs. I think the real reason why we don't see large TPUs is because nvidia cards has had tensor cores built into the architect since Volta and with a GPU you don't have to worry about system memory speed since you have 80Gb of HBM.