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You're misreading it.

"Destructors are invoked implicitly for constructed objects" … meaning those that exist and their existence has gone as far as complete construction. Although arguably not entirely spelled out, the original A does not meet this criterion as it is no longer "constructed": it does not exist at all! Only the new/replacement object is automatically destructed, then, at the end of main, as you'd expect.

Otherwise, this form of placement new would be pretty dangerous and of debatable value in the language. However, it's worth pointing out that re-using an actual A in this manner is a bit strange and unusual, if for no other reason than it leads to just this sort of question. Typically you'd placement-new into some bland buffer (like a char[N] or some aligned storage) and then later invoke the destructor yourself too.

Something resembling your example may actually be found at basic.life¶8 — it's UB, but only because someone constructed a T on top of an B; the wording suggests pretty clearly that this is the only problem with the code.

But here's the clincher:

The properties ascribed to objects throughout this International Standard apply for a given object only during its lifetime. [..] [basic.life¶3]