>>5012181hypothesis/conjecture:
You can have cheating without netorare, but not the other way around, and I suppose that is because of how netorare is structured.
In a story that has cheating but not netorare, the character being cuckolded is not important to the story, he/she is not being thought of much or at all by the other characters, and may never know about the affair.
In netorare stories the one being cuckolded is in someway important, on the mind of one character or another until a character arc (normally mindbreak) is complete, he/she finds out and then is involved the plot in someway, or simply reacts to the cuckolding in any manner at all.
Self insertion is not necessary or even intended in the creation of netorare stories, and may not be done by the audience. But, said audience may still be upset by the work without having to self-insert or from moral outrage, but upset by how the story is structured. This reaction could be attributed simply because art and media can illicit emotions simply by their consumption by a human mind.