Yesterday was for all the saints: all the people, according to the Catholic Church, who have performed enough miracles to get canonized.
Today is for all the dead people (or what’s left of them, i.e. their souls) who aren’t in heaven yet. They’re in Purgatory, and we’re supposed to pray for them so they can get out.
But what about all the good but not-quite-saintly souls who’ve actually made it to heaven? I think the Church needs to perform its syncretistic magic on the Day of the Dead. Maybe they could put it on top of Halloween, since All Saints Day doesn’t seem to have worked too well.