maildir? Uh.... Since we're telling jokes:
It was not a joke, and dismissing it as such is a very unkind form of communication. But next time, please find a funnier joke to retort.
As for using a much "simpler and already implemented" standard, where was the existing standard formats that could handle everything that a Word, Excel, or Powerpoint document could contain? To use any of the existing formats would make it impossible to save documents in those formats without losing formatting and/or data.
I know nothing of the process that happened to get these specs produced but I think it's pretty reasonable that Microsoft would want to make sure the formats were capable of storing the existing Office document capabilities completely. Think about it, if they had settled on anything less then customers that used any of the unsupported capabilities would not be able to use these new formats.
It's easy to find material on the process. Your argument is correct; that happens most of the time when you change formats, but nobody would have forced Word to exclusively use the new format. I am sure your thoughts played a role in Microsoft's actions, but it just explains in more detail why they were not interested in "standardization" in the meaningful sense of the word.
Standardization means, at the very least, to also abstract to identify essential concepts, generalize them, document them systematically etc. But what Microsoft did was "take what we already have and describe every detail", and in fact, there are numerous places where the same concepts are described in several unrelated parts of the spec, and specified in different ways.
They had been invited to the standardization track of the OpenDocumentFormat. They declined, because they thought that with their market domination, they could force anybody to use their formats, anyway. When the ODF process gained traction and industry supporters, they started the OOXML campaign in all its aforementioned vileness to get "their own standard". Which they did, and "their own standard" it is, in every sense of the word.
Regarding the size of the specs, yeah - they're big. Did you happen to notice that about a third of the size is image files? These docs cover the XML specification for every single thing that you can have in a Word, Excel, or Powerpoint document. You may not realize or appreciate the breadth and depth of what can be encapsulated in those documents, but it's a lot. A whole lot.
The difference is that you regard this as a feature (or as Microsoft catering to their users), I see it as the main problem (and Microsoft just continuing forever with whatever they started to not lose any locked-in customers). As for images.. the argument still holds if
half of the size were images.
Just curious - have you looked at the size of other document specs? The HTML spec is huge - 20MB+ the last time I downloaded a copy. The CSS spec is painfully large and terse. XML, XSL, and friends make CSS look like a quick read. And so on. And this is a good time to point out that these open document types are fine examples of formats that only a huge company or other large group of developers could implement.
Of course I have looked at many specs, as part of my professional duty. You cite good examples of similarly atrocious specifications. And accordingly, at least HTML+CSS etc is now equally impossible to implement without vast resources, which is the main reason that there are so few browser rendering engines left, moving swiftly to a monopoly.
It appears to me that you think that the software mentioned above has great value to humankind, hence it's not only ok, but rather mandatory that we keep all its features (and hence, also incorporate them in "standards"). Well, we'll have to agree to disagree on that.