In addition to what's been said, he also hasn't had a respectable season since 2000 and is 36 years old. Kemp's game was based on freakish athleticism. How many freakishly athletic 36 year olds can you name? How many of them had serious drug and weight issues? Kemp's finished, and he's been done for a while. This happens every year; a washed-up player who used to be good expresses an interest in playing again, and people on this board say we should give him a shot. Last year it was Rodman, the year before it was Isiah Rider... Who's next? Maybe Sprewell a few years from now?
The Sonics were also somewhat of a rival back when he was playing well. Not nearly as much as the Jazz, but a rival nonetheless.
Losing 70 pounds in 6 mos is too much. Most likely quite a big portion of it comprises of water loss and muscle loss. Not good.