I have ghostwritten an amazon bestseller before, and it is about selecting a title and cover that appeals to what people are searching for. So there may have been a product-market mismatch when the poetry book was launched. I think books on Buddhism, especially targeted to beginners are rather popular these days when the title is clear on what it is meant to advice on. If the message on ecstastic buddhism ever spreads, it is likely via this avenue, given that the alternative are books like TWIM (bhante vimalaramsi), corrupted teachers like Culadasa, teachers stuck at elementary understanding, etc.
Books like the Nikayas are also very popular but the translations are questionable, given it is usually by Thanissara Bhikkhu. Online published version at suttacentral.com also has wonky translations.