Why can't teens we make in other active households spawn as high school classmates?

I have an entire save full of teens. 4 boarding school/ communal teen homes with 5 in each not including teens still with their parents and of course pre mades. At first this annoyed me but then a few of my teens came to school as npc's and it affected their relationships and performance as a few fights broke out or their manners and empathy dropped etc. In essence since I couldn't control them I'm fine with them not coming. If I want certain teens to go to school together I just swap household members briefly. I think because I have so many I'm likely more okay with them not showing up.