I have several theories on this but mostly that publishers and editors are all writers of some sort or another and none of them understand marketing. The only thing they know is what has sold in the past.

The problem with the publishing industry is that they suck at marketing. Writers, like most artists, suck at self promotion.

My theory is that the publishers have abdicated responsibility for promoting anything because they don’t know how, so they pushed it to the authors so they can blame them when it doesn’t pan out.

This is 35+ years of marketing experience talking.