Sheol and paradise seem to be later developments; it became abundantly clear, when you sat back and looked at it, that people's just rewards didn't necessarily come in this life. This frustrated the writer of a number of Psalms, as I'm sure you know.
The later addition of ideas about some kind of afterlife was the sticking point between the Sadducees and Pharisees in the gospels - the former only accepting the afterlife-free Pentateuch as Scripture.
Theology evolves through the Bible. It's an interesting topic.