Clothing patterns come in different sizes - sometimes only one size per envelope.
Perhaps a quilt pattern can also be drafted for different sizes and sold in different envelopes?
I know that knitted and crocheted items sometimes do have multiple sizing in the directions.
For some, following the instructions for the given size for a pattern is confusing. More options would just make it more problematical for them.
IF one decided to do multiple sizing for a pattern and several sizes came "in one envelope" - it would be reasonable to charge more for the "package"