Your statement is incorrect system wide. It may be correct in your category. In general it's easier to build trips with minimum credit with longer trips. This is especially true when you have cities that require 30 hour layovers.
I suspect in your category if they did away with 4 day trips and went to all 2 day trips credit would soar. There are always shorter trips that can be built without credit. Building entire categories based on shorter trips with no credit increase is not workable.
The company has always been receptive to suggested scheduling changes even when they involve some increase in credit. That is why we have the survey out now. When you have a change however you have to show the effects. When you take concepts to reality the results rarely match what pilots believe.