That assertion completely misses the point. The scenarios involving move constructors throwing exceptions involve objects being stuck in an inconsistent/zombie state. In fact, the whole point of a move constructors is to avoid having to allocate memory.

Folks might be using mmap with MAP_POPULATE; they might have overcommit turned off; they might be operating in an rlimit/cgroup (like most container runtimes/orchestrators configure) that limits memory; they might be on a system which doesn't have virtual memory (plenty such systems exist in 64-bit architectures); they might be using calloc on an OS that zeros pessimistically/early; and so on.