And yet there’s plenty of adult coloring books made by a human out there if you’re willing to go to a brick and mortar shop. Got a super cool one from dick blicks, with a lot of underwater scenes. Also paper quality is important. I can’t imagine getting as far as I did in mine if it was newspaper

That’s because those are not personalized. The economy of scale allows for artists to make generic coloring book with high quality art, but it’s expensive for artists to create (and customers to buy) custom made coloring books personalized for the customers photos.

My partner makes one! Go grab a copy if you're in Australia, the wonderful POP local -- started as POP Canberra -- sells them.

https://www.poplocal.com.au/product/bum-man-colouring-book/

He's 'Bum Man'. A man (actually it's asexual) who is a bum. I mean c'mon.