Who actually decides on the best project ideas?
“Detail as you go!” saves energy and capacity.
Project proposals “mature” as they move through the funnel. They are regularly reviewed and revised, if necessary, as they move through the phases. At each stage, only that information is needed to decide the transition to the next stage.
Also, at the end of a stage of the portfolio funnel, only the project details that are really needed for the next decision or ultimately for good preparation and a safe project start need to be available.
Therefore, the committee deliberately avoids too much detail in order to make decisions efficiently.