Why asian people from central asia and north east russian have big cheeksbones and jaw than other asians?

why asian people mongolia, some kazakh who has strong asiatic heritages and indigenous people of east soviet. for example Nanat, yakutian etc have super large cheeksbone, sometimes jaw too than normal east asian and south east asian? also south east asian in general have oval face than north east asian. except the ones who have chinese-mongolian blood like laotian and hmong.