Since RAWs are just the RAW take from the sensor and some extra metadata usually it would be the reverse... a JPEG requires more processing to generate. Though a RAW requires a higher datarate to store an image.

I think it's mostly that most people don't care enough for RAWs. I tend to shot in both RAW+JPEG(at max quality) if I like the JPEG I'll keep it if not I'll try playing with the RAW to see if I can get anything out of it.