Google has their own TPUs so they don’t have any vendor lock-in issues at all.
OpenAI OTOH is big enough that the vendor lock-in is actually hurting them, and them making that massive deal with AMD may finally push the needle for AMD and improve things in the ecosystem to make AMD a smooth experience.
Having your own ASIC comes with a huge sunk cost. One gets advantages from that, but it's still a lock, just a lock of a different color. But with Google money and manpower, management can probably pursue both paths in parallel and not care.
I can assure you that most internal ML teams are using TPUs both for training and inference, they are just so much easier to get. Whatever GPUs exist are either reserved for Google Cloud customers, or loaned temporarily to researchers who want to publish easily externally reproducible results.
OpenAI OTOH is big enough that the vendor lock-in is actually hurting them, and them making that massive deal with AMD may finally push the needle for AMD and improve things in the ecosystem to make AMD a smooth experience.