It's not All the Rest of the Saints Day, as though we're trying to be fair to everyone in heaven who doesn't have his own proper office.
It's not Each Saint's Day, as though we're praying, "We rejoice in you, and you, and you, and you, and you, and you, and you, and you, ... and you, and you there in the back. Let's see, is that everyone?"
It's All Saints Day. The whole, not the parts or the individuals. And yes, the whole comprises individuals, but the saints in heaven compose a reality that is more than the sum of their individual persons. Together, they are the Church Triumphant, and as the Church they offer acceptable worship to the Father through the Son in the Holy Spirit.
This is one of the great both/ands of Catholicism. Today we celebrate both each saint and all saints, with the celebration of each saint placed within the context of the celebration of all saints.