Suppose we require it that the output flush must take place before the behavior becomes undefined by a bad division. That doesn't buy much because the visible effect is only that some bytes are passed from the stdout stream to the host environment. The undefined behavior is allowed to bring down that entire environment though; so our requirements don't add up to the certainty that the output has been transmitted out of that host system to some output device (display, serial or network, ...), or committed to durable storage. (The latter could be wiped out by the UB, even if so).

Basically, standardization groups should be dissolved long before they devolve into stuff like this, where they are just creating churn for the sake of their own continuation.