"Why isn't AMD trying to reach this market?"

https://en.wikipedia.org/wiki/Zen_(microarchitecture)

AMD would still have an AMD64 architecture though? Or are you thinking they should come up with a new competing architecture.

These POWER chips are an open design; thus, anyone who wants Google as a customer and has a chip fab ready to go (like, say, AMD) could, in theory just fab some up to sell to Google.

AMD doesn't have a chip fab - they are fabless now.

Oh wow. Is there a good reason for this?

Maintaining a fab when you can't justify enough orders for chips to keep it running around the clock is expensive. As part of the spinoff they had penalties because they weren't purchasing enough wafers from GF anyway, but it resulted in less bleeding than owning and managing it as a subsidiary.

They're broke and they need at least $750MM to $1B in the bank to operate effectively as a company.

Neither does IBM as of last year - all IBM POWER chips are fabricated by GlobalFoundries.

Are you sure? Global Foundry is owned by AMD, no?

No, it was spun off. AMD initially retained a minority stake, but sold their remaining shares a few years ago.