I think the appeal of oniiloli/oneeshota is putting yourself into the role of the male and being enamored by a cute girl or beautiful woman. Unfortunately I can't relate most of the time because I... Don't want to self insert. I want to be invested in the relationship between two or more ppl but it's kind of hard when only one of them actually exists. The counterparts to these don't tend to do that so I end up enjoying those more. Same with kemono, probably cause those have more species that the artists wants to draw