What would the Creator do with all Individual Intellects who choose not to develop? They don't fit in the Ultimate Goal of the universe. Will they be allowed to co-exist with the elevated Intellects, will they be exiled, or will they be terminated?
Everything that we see in Nature around us is continuously re-cycled, by Design. The most logical choice would be to erase all memory and let those intellects start over from scratch. Isn't it happening here already?
Coexistance: suppose that a few babies are allowed to be present at the University lecture. Do you think that teaching and learning could proceed when babies start playing and crying? Wouldn't the entire process of study be interrupted?
For this very reason - there HAVE TO be grades at every school. Also, there are several grades/categories of planets (see The Book for details).