First, when Michelle started doing events like SA, there was no such thing as the GP. Kwan started doing them at the end of '93; the idea of packaging six of these events into a series with points leading up to a final didn't exist until 1996. Also, it wasn't until 1996 that they even offered prize money at Worlds. So, when Michelle was in the same place that Kimmie and Emily are now, she wasn't lining her pockets by competing. Second, the fact that Michelle and Sasha earn money by touring and endorsements are good reasons why they should NOT do the GP. Let the skaters who don't make touring money, and need the prize money compete.
Third, and most important, is that Michelle and Sasha will get nailed no matter what . When they don't compete, they get accused of selfishness or greed. When they compete, they (especially Michelle) get criticized for not letting other skaters have their time in the spotlight. After all, last season, the failure of Michelle and Sasha to do the GP meant that American TV audiences got introduced to other skaters, such as Joannie Rochette, who would not have gotten the exposure if Michelle and Sasha had been there.