Typically, it is there to create a sense of permanence to the characters that are created. It is also meant to help prevent people from abusing parts of the game that depends on probability such as force sensitivity.
Without a three week period you would have people killing off their characters over and over in order to become force sensitive. Of course, this is only one of the many reasons there is such a long wait and as mentioned already it will most likely not change which many people, this one included, seem to prefer as it does give a sense of permanence which is quite nice.
Once full combat is implemeted, and death is more common, it'll be changed. However, right now, it takes a lot of work to die, and as such, given how our characters are "Permanent Death", the wait to come back is a finalizing aspect of that characters death. It's a detterent to non-chalantly just offing your character whenever you want a new name/