As you state yourself, cs degrees fail at being proof of competence. They are too long, expensive, and unfocused. Hence why we really could use something else, simpler and more accessible.

Yeah, but which institutions would design such exams? CS degrees aren't ideal but at least they're designed by people who have CS training and are programmers. If a government decided to set such an exam it'd probably end up requiring some sort of certification in enterprise .NET development.

Accountants and lawyers manage to set their own standards, surely developers can do that too.

Maybe. I agree that's a strong argument, but I think for both accountancy and law the standards are in both cases defined by governments, as the professions are largely about ensuring compliance with what governments require. The professional certifications can thus be just checking your knowledge of what the rules say, without getting into the question of whether the rules are correct.

In software it's not like that. There are very few laws on the book about how to write software, so there's no single authority that defines the right answer or the scope of reasonable questions. It's far more open. Even just picking a set of programming concepts would immediately cause controversy. Like, should monads and type-classes be a part of the professional qualifications? Most programmer would say no, because Haskell isn't widely used in industry. But CS degrees do sometimes test people on that sort of thing!

This seems like a decent point for accounting but not really for law. Certifying a lawyer is not just about a finite set of things they have to know, it's about fundamentals and the ability to ingest facts and form an argument. Similar to your Haskell point, there are parts of the law that not all lawyers need to know, but are expected to be able to figure out as needed and the certification aims to check for that ability.

(Also, in both cases, the government hires members of the profession to define the standards.)

I'm convinced we could have a bar exam for software engineering, but I'm not at all convinced that we should. It would make my life easier personally, but it would keep a bunch of people who followed less traditional paths out of the industry and I think that would be bad.