Pornography is not a genre

Pornography is orthogonal to genre. Defining porn is notoriously difficult ("I know it when I see it." Thanks a lot, Justice Stewart...) but a decent working definition is that if a work is composed around a requirement to present material that is intended to be arousing to somebody, it's porn. But the supporting framework, if it exists at all and if it forms a narrative, can be of any genre at all - and because porn "pays its rent" with the sexy stuff, that supporting framework can also be wildly more experimental and strange than any narrative in a commercial work. In fact, every aspect of porn, from composition and layout to plot and characterization, is allowed an arbitrary degree of freedom as long as it doesn't interfere with the delivery of the payload.

This means that porn can be extremely lazy and uninteresting outside of its intended purpose, sure. But it also means that porn is fertile ground for artists working on their craft and their ideas. In the US, there's a stigma that attaches to any artist who has done porn, but in Japan, among other places, it's the breeding ground (if you'll pardon the expression) for many a talent who then breaks into the mainstream using what they developed in the doujin scene. Shun Saeki released two volumes of porn before being hired on to draw the wildly successful Shokugeki no Soma series. Johji Manabe has wandered between sexy adventure stories and porn with plot for his entire career. Okayado and Kohta Hirano basically debuted by expanding on their porn stories' plots with less outright fucking. And I'm sure I'm just scratching the surface here.

And porn really does transect all genres. I've read porn comedy and porn tragedy, porn horror and porn farce, porn romance, porn slice-of-life, porn mystery, porn science fiction, porn fantasy, porn propaganda, porn cautionary tales, porn folk tales, and porn I-don't-even-know. There's porn in genres and styles I'd never read if it weren't hot, and there's porn I read even though it doesn't do a thing for me because other aspects are so compelling and because it delivers the kind of weirdness I'd never be able to find in a work that has to justify itself by any other means.

Porn isn't a genre. It's an axis of constraint that grants freedom in every other direction.