Goris describes how romance covers are deliberately made to look superficially the same to the general public (e.g. semi-naked clinch) but include subtle differences that romance readers can decode (e.g. gal in leather pants means paranormal). (A "double semiotic code")
She goes on to say how the generic features are necessary for non-romance readers to distribute, acquire and generally support the delivery of romance from the people who make it to those who read it, by those who don't give a crap about it. And these cues have to be very unsubtle because romance fiction is sold not only in bookstores but a wide variety of other general retailers.
Because these deliverers of product are not interested in, or educated about, genre romance the cover art has to be very uniform and overt for them to get the message. And this in turn creates and reinforces the general impression of romance as "...formulaic, overly sexualized and more than a little ridiculous" and gives an impression of low quality** assembly line production. Especially as non-romance readers are not able to decode the subtle variations that indicate what is distinctive about each title.
So basically the argument is that the clichéd and repetitive part of romance covers that the general public disdain, are made that way because the general public does not understand anything more subtle--and romance fiction requires these people to understand how to transport, stock and sell it. While romance readers benefit from the publishers ability to encode nuanced detail on top of this standard template.
Or as this is phrased in academic-speak***: "...far from being a random or coincidental effect, this semiotic pattern is a deliberate strategy ... public intelligibility of its material code is an important consideration for a book that circulates in a wide variety of cultural and commercial spaces..."
* "Hidden Codes of Love: The Materiality of the Category Romance Novel" by An Goris
** See: Romance, gender, and the measure of a 'real book'
*** (Because while romance needs to be easily recognized to be effectively traded, academia only respects maximally pretentious phraseology.)