Genetics, lack of breast feeding, soft foods, etc probably influence poor jaw development. Also mouth breathing due to allergies and nasal blockages, bad tongue placement, probably other factors. My snoring improved a lot in adult years when I learned to keep my mouth closed and breath through my nose. My tongue position was so bad that an ent suggested tongue ablation, but instead I learned to deliberately thrust my tongue against my palate. It's difficult because in childhood I basically learned to mouth breathe because my nose was always blocked. That probably caused a lot of my problems with cavities and poor jaw growth. I was also bottle fed mushy foods for the first few years, instead of having more solid foods. I did use a night palatal expander as a kid, but wasn't too consistent in turning the key and my parents weren't really persistent with it.