I have a theory based on nothing at all:
1. want all beginners to make a quit together
2. count # of beginners and desired quilt size, decide on 6” blocks
3. Choose a “beginner” block for the quilt (disappearing 9-patch)
4. unable to find instructions for a disappearing 9-patch that makes 6-inch blocks, do not ask yourself why that may be
5. ask someone to manually calculate the necessary cutting instructions