...because there is plenty to do. There are plenty of things to do that don't use fastpass, especially at AK and Epcot.
Sure....those things used to be the a, b, c level attractions ticket attractions. Not things that were designed to get you to come to the parks, but literal filler. At the end of the day Disney does not have enough big ticket items to support a fastpass system for all guests. By making fastpass access easier (fastpass plus), it just magnified how much thats really true.