dict is not a function, it's a class and the purpose of a dict() call is to create a new instance of that class.

The change you are proposing is also breaking for iterators:

>>> class Pairs(list): pass
... 
>>> pairs = Pairs([('a', 1), ('b', 2)])
>>> pairs.__dict__
{}
>>> dict(pairs)
{'a': 1, 'b': 2}

A change of this magnitude will need to be discussed on python-ideas and will require a PEP explaining why the benefits of the change outweigh its costs. I very much doubt that they do.