OK. its a bit extreme, but I think about it as RAW="negative" JPG="print".
The prints may be stunning, but, if you haven't kept the negative, you can never go back and create a fresh print.
So why might you want to create a new print? Sometimes your initial thougts on the pic change - I've often gone back to an old image and decided it was better "printed" darker or lighter. Also every month we see new processing software appear - I like to be in the position to go back to older images and perhaps improve the sharpening or reduce noise a little more.
While you can of course re-edit a jpg, it is important to realise the jpg processing is destructive - every edit you make is throwing away irreplaceable data. Sort of like scanning a print to edit the image (OK, I'm exaggerating for effect
Colin K. Work, Pixstel