Shipping and tax mainly. What I hope to put into readers' hands for
about $15 ends up costing them $30-$40. Physical distribution still
seems a mess for small publishers who are in that gap between full
POD/Lulu type thing and working with a major brand.
For example, many distributors won't take on business with publishers with less than 5 or 10 titles. Mine has 3, so is considered a "vanity press". Coordinating POD internationally is a PITA. So I use a smallish UK POD (Great British Bookshop) of my current project, and hold a few dozen myself mainly for mailing out to reviewers and press. Also, lots of distributors still operate on "store and forward", which means holding litho-printed stock (runs of 500+). I just can't be doing with that in 2022!
I also recorded an audio [1] version, which has had precisely zero sales AFAICT, mainly because I have no idea how to break that market.
Any podcasters here wanna give it a listen? shoot me a message, cheers.