As I always say, no award is given in a vacuum.
Decisions made in each race in those 30 years between Oscars always relied on competition in the fields. It's always subjective. (Warning: here be personal opinions.) Sometimes better performances beat her (Susan Sarandon in DEAD MAN WALKING or Hilary Swank in BOYS DON'T CRY), sometimes leads of better films beat her (Gwyneth Paltrow in SHAKESPEARE IN LOVE), sometimes legends whose time had come to win (Helen Mirren in THE QUEEN, Sarandon as well), in every race the field has a different feel and is shaped by many variables.
There is no "they" and there is no overarching plan to how Awards will be given out in one's career. Streep very well could win an award for this; it's a hell of a role, she's a hell of an actress and we haven't seen it or really any of her likely competitors, save sparse exceptions.
There is so much that could happen, this far out, that the only thing with certainty that it's safe to argue about the Oscars is that arguing something with certainty is lunacy.
Words don't deserve that kind of malarkey. They're innocent, neutral, precise, standing for this, describing that, meaning the other, so if you look after them you can build bridges across incomprehension and chaos. But when they get their corners knocked off, they're no good anymore…I don't think writers are sacred, but words are. They deserve respect. If you get the right ones in the right order, you can nudge the world a little.