It seems to be a thing, apparently, but maybe it's also something cultural in the East Asia? Like, I've read mangas, manhuas, and manhwas depicting girls/women wearing bra while sleeping.
I'm glad this got serialized so I could get it in print and support the author, but I prefer the simplicity of the original Twitter version of almost all of these comics. I liked the mystery of Sakura's background and the lack of an overarching narrative.
This felt a bit on the nose, as it tried too hard, unless it wasn't literally her sitting on the floor in a corner, or everyone, including adults, avoided her for some specific, not officially announced reason.
Considering what we have seen of her background so far it's not surprising that she fell so hard for someone who treated her nicely and as a human being.