A Brazilian CA trusted only by Microsoft has issued a certificate for google.com

This is a bad look. I expected the result would be Chrome and Firefox dropping trust for this CA, but they already don't trust this CA. Arguably, Microsoft/Windows trusting a CA that the other big players choose not to trust is an even worse look for Microsoft.

What is even the point of a web CA that isn't trusted by all of the major players? Is there one?

These are generally government CAs, so, typically the situation is Microsoft sold the government Windows, and as part of that deal (at least tacitly) agreed to the CA being trusted, and so every system that's trusting these certificates is a Windows PC anyway, running Edge because the whole point was the government will only use Windows and pays Microsoft $$$.

Why bake it into everybody else's Windows? If you make say a Brazil Government-only Windows which trusts this CA instead, I guarantee somebody crucial in Brazil will buy a 3rd party Windows laptop independently and it doesn't work with this CA's certificates and that ends up as Microsoft's problem to fix, so, easier to just have every Windows device trust the CA.

They'll have an assurance from the CA that it won't do this sort of crap, and that's enough, plausible deniability. Microsoft will say they take this "very seriously" and do nothing and it'll blow over. After all this stuff happened before and it'll happen again, and Windows will remain very popular.

Windows CA program is governed by requirements like any other CA. Microsoft has ways to provision machines with enterprise CA roots so there is no advantage, and highly visible disadvantage, to adding a noncompliant CA to your trust store. I think that the theory that Microsoft will included it to sweeten a sale has no merit, unless you have evidence.

Most certificate trust stores have some certs in them that are sketchy, eg a bunch of university certs from all over Europe. These are slowly dropping off, presumably because it costs quite a bit to operate a CA in a compliant fashion and get it professionally audited.

Issuing a fake cert is grounds for removal from every certificate trust program I’m aware of, if it can’t be demonstrated that they found what went wrong and have fixed it so it can never happen again.