BTTF actually connects really well with the Matrix in that sense. If either were written in advance to have following chapters, the creators would have ended the first movies in a very different way. They both have a sense of "our story ends definitively here, but our hero's adventures continue, enjoy imagining them for yourself!" Even the original Star Wars movies have that, if you look at how the movie eventually retitled "A New Hope" ends, because there was no guarantee of a sequel.