Hi Scott. You have asked how does this story work, after making a critical point that Roma is not so much focused on a main protagonist per se, much more with defined wants (or motivations, if you prefer). This point makes me think of a couple of things, how, especially we can be conditioned to look for the shape of a story, especially in a film. I would say we are conditioned as Americans, by Hollywood’s long standing obsession for churning out story after story for decades, that have the major plot mechanisms, like, inciting incident, turning points, and so forth. And yet, mechanisms is a very accurate way of describing what these stories do for us as an audience. Watching films can be a visceral experience, and without waxing too philosophical, one cannot help but reflect that these mechanisms are pushing our buttons as audience members. That is, feel pity here, feel joy there, begin with story here (inciting incident).
That said, Roma came across as less a narrative than a sort of continuum of a time past, even if it was mostly a work of fiction . It has the spirit of a sort or cinematic remembrance of things past.
Lastly, I am reminded of an interview that Godard gave on the Dick Cavett show where he declaims that we Americans just produced “stories, stories, so many stories” and that he could hardly fathom that as a European filmmaker.