That was my thought as well. which surprises me because based on known time lines and the fact that Apple debt was mounting he would be (and was) the savior.
But we don't know what made him do it
I am still not sure either. I know the court battles were driving both of them crazy and so I guess Gates finally let Jobs convince him to just end it. That's what I say but I really have no clue why Gates did what he did and saved the company that really beat him up for many years.