Yeah, when the girl was like down knowing that Wataru (seme) makes his own lunch, I was like wtf's wrong if a man or you make your own lunch? Lol kinda off putting how the author wants make it as considered "weird".
This is a mix of what I know and what I read in some other manga's (so it's probably not that reliable, it could be just a trope or whatever), but it's something along the lines of- some japanese girls find it burdensome knowing a guy can cook a full on bento with decor like that because of all the effort and time put into making it. In Japan, girls/housewives are the ones who usually make bento for their boyfriend/husband, so when single men can do it themselves with that much effort, the girls would feel burdened to match or go beyond that level of effort
This man is self sufficient and the author wants to portray that as a weird thing that puts women off? Bro, a man who cooks is a win win scenario. Japan wtf (￣∇￣"). https://www.mangago.me/read-manga/happy_end_wa_goisshoni/uu/to_chapter-1/pg-5/