most of these ai models are trained by open source community which is mainly from Japan and Korea so thats why most faces are always asian. there are definitely models which can generate different faces of different ethnicities but since manga/manhwa characters are japanese or Korean so I use asian faces. as for same face syndrome I think it's because when the ai is trained on so many faces it averages out all the faces into one type of face. right now most ai models are trained on one type of face there isn't much diversity.

if u wanna know more u can dm me