MSFT or even Google (AWS is not as mature in that space imho) made perfect sense, Oracle doesn't.
Elon and Larry are good friends, I would guess that has something to do with this development.
And the market leader is what, 30%? about 1 order of magnitude. That's not such a huge difference, and I suspect that Oracle's size is disproportionate in the enterprise space (which is where a lot of AI services are targeted) whereas AWS has a _ton_ of non-enterprise things hosted.
In any case, 2-3% is big enough where this kind of investment is 1) financially possible, 2) desirable to grow to be #2 or #3