create_directories may need to create temporary paths, and remove_all may need to create temporary paths and/or directory_iterators. These operations may require a potentially throwing memory allocation.

Implementations of copy_file may wish to dynamically allocate the buffer used for copying when the underlying OS doesn't supply a copy API directly. This can happen indirectly, e.g., by using <fstream> facilities to perform the copying without supplying a custom buffer. Unless LWG wishes to prohibit using a dynamically allocated buffer in this manner, the noexcept should be removed.