There happens to be more quality literature in the grade 4 and 5 levels because of YEARS of composers writing for collegiate level groups or higher. Give it time. They are adding a lot in the lower grades every year. Also, a lot of the composers that started out writing for lower grade music are now writing harder music. I’m thankful that some, like Randy Standy, have gotten into more difficult music AND are continuing to write for lower grade levels as well. Not always the case.