I guess they wanted to emphasize the relationship between Hanbit and Woojoo (before all that) and the feelings Hanbit had for Woojoo, which was mostly cuteness aggression separate from the feeling of being hrny. Like, I have a cuteness aggression toward dogs, but Lycaon from ZZZ is very attractive so whenever I look at his abs, I drool, but the moment I see his face, my heart fluffs up and I get the urge to pet it (I'm not a furry, he's an exception). I don't know if you'll understand what I just said since it's more of a blabber than a proper response.
Also, I think it's just the art style that makes them look like children, and yes, Hanbit included.

They are step brothers but that’s not what made me stop reading. What got me is how the author makes Woojoo child-like. Like wearing the underwear he wore as a kid(?) or around chapter 32 where he’s in ML’s shirt and looking like a child. Even ML makes comments about him being young and getting himself into trouble. I’m not sure why Author is leaning into this aspect so much. Without it, I think it would be a more palatable read. Thoughts?