You can always just use password unlock. Face ID is not a requirement to use the phone. It’s just a convenience. As to why the in screen fingerprint reader is

You can always just use password unlock. Face ID is not a requirement to use the phone. It’s just a convenience. As to why the in screen fingerprint reader is not an option, obviously there was some sort of conscious decision to not go that route. I can’t tell whether that decision was motivated by money or by desire for good UX. Probably both