$20 is a pretty typical price for sewing patterns. They’re a lot of work to create, and you can use them as many times as you want.
I'd also like others to be able to do the same, so I can get their modified versions. Usually, someone else will solve my problem.
I don't mind $20, but I do mind needing to pay $20. There are lots of companies who make great patterns. I'm not sure what makes this any different.