I believe it's actually the opposite. You're supposed to be able to reuse objects that were moved from unless otherwise documented, although it may require reinitializing it explicitly. A moved from vector is valid to reuse. Although the standard doesn't specify what state it will be in, all major standard library implementations return it to the default constructed state which doesn't require an allocation.
Read what I wrote again. I said all member functions.
Reusing of a moved from object only requires assignment and destruction to be well behaved.
The std library containers give you extra guarantees (a moved from object is effectively the same as a default constructed one), but the _language_ imposes no such requirements on your types
It's perfectly allowed by the language for the .size() member of your own vector type to return a random value after it's been moved from because you wanted to save 1 CPU instruction somewhere.
I understand what you're saying but no major compiler does anything nefarious. They default initialize it. A lot of code depends on std::optional that was moved from returning false for is_valid for instance and no one would break that even if it's not guaranteed.
