> But who would go through the pains of manually making up a mushroom identification book, while perhaps being quite clueless about the topic, on the faint hope of selling a few copies

Err, at least 1 person: English As She is Spoke[1] was published in 1883 and was a lot more involved (lots of literal translation by an author who didn't speak English)

1. https://en.wikipedia.org/wiki/English_as_She_Is_Spoke