I wonder if the lack of Joe is out of respect - recognising he didn't do anything to warrant being viciously dragged for. Like how she said she writes bad men the best (not sure exactly how she worded it), and he isn't so was mostly absent. Though if so, still kinda mean she let her fans get carried away with the idea it would be about him/him cheating. So not as if he got away unscathed.
Or could be out of spite - e.g. you're not important enough to mention.
Or she's still dealing with her feelings. Or she saw midnights as the album to process her feelings on him. I have no idea!