How come there’s ASICs for mining but not AI? Seems like there would be almost unlimited demand

There is. It does 16k tokens per second. https://chatjimmy.ai/

Weren't the Google TPU stuff that already? Wikipedia says that's from a decade ago.

Mining is all compute and no IO. Training particularly is heavy compute and insane IO.

There are asics for ai. They're called gpus / tpus.