This is like getting mad at ISO 8601 because it doesn't define the metric system.
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.
A better situation than today would be only having to deal with Microsoft and Not Microsoft, rather than multiple different ways of handling the problem that can differ unexpectedly
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.