The ABI mess predates the standard by years and if we look that far back the Annotated C++ Reference Manual included a scheme in its description of the language. Many compiler writers back then made the intentional choice to ignore it. The modern day ISO standard would not fare any better at pushing that onto unwilling compiler writers than it fared with the c++03 export feature.

When you have one implementations you have a standard. When you have two implementations and a standard you don’t actually have a standard in practice. You just have two implementations that kind of work similarly in most cases.

While the major compilers do a fantastic job they still frequently disagree about even “well defined” behavior because the standard was interpreted differently or different decisions were made.

No standard stands alone in its own universe; complementary standards must necessarily always exist.

Besides, even if the C++ standard suddenly did incorporate ABI standards by reference, Microsoft would just refuse to follow them, and nothing would actually be improved.