Because depending on what I'm sharing and with whom, I may not always want to send 30+ MPix images if I know it's going to be viewed on a phone/tablet or downloaded from a data network (typically, family reunion stuff that nobody wants a 15MB ultra sharp file of). If the photos might end up on the open internet, I don't necessarily want my camera's serial number and other "global IDs" present in the EXIF to be kept, but I might want to share "straight out of the camera" JPEGs with full metadata with my photography enthusiasts friends. That's one area of the workflow I feel I want to be in control, because it is very contextual.