It makes far more sense for Amazon to prop up an OpenAI competitor to secure access to state of the art models for AWS. Amazon doesn't compete on excelling in AI.
AWS and Google Cloud invested in it for exactly the same reason, to enlarge their cloud businesses. Googles previous investment came with a cloud partnership, then AWS also gave them a cloud partnership, and now Google strengthened their cloud partnership to ensure AWS doesn't take it all.
So this bet doesn't have anything to do with AI, it is a competition between AWS and Google cloud. They are competing over who gets to sell shovels in a gold rush.
But Google is very fragmented as I said, what cloud does has little to do with what other parts of Google does. This investment makes sense for cloud so they make it. It is a weakness and a strength of the company, Amazon is much more top down and that leads to other problems.
