https://mail.python.org/pipermail/python-ideas/2017-December/048489.html

Guido is waiting for objection on this...

I have absolutly no idea why this decision was made.

These tests (ttps://github.com/python/cpython/blame/master/Lib/test/test_collections.py#L794):

        non_col_iterables = [_test_gen(), iter(b''), iter(bytearray()),
                             (x for x in []), dict().values()]
        for x in non_col_iterables:
            self.assertNotIsInstance(x, Collection)

were written by Guido himself.