I actually think Michelle could've been bigger if she had a bit more spark in her personality. She was always very gracious and sweet, but not really a natural media darling (and I think Lipinski really capitalized in 98'). Now, Katarina Witt was someone who really had the personality to sell herself as a star. But it's true, in the US, you really can't become a star just by being a good skater. You have to cross over into other media stuff to get anywhere. Star power also builds on tabloid potential and a lot of skaters are just rather dull compared to the juicy stuff we get from actors, musicians and other sports figures. I think it's similar to female gymnasts - they get a lot of attention during the Olympics and then no one cares for 4 years.
I think Michelle did about as well as she could have, given her training schedule and the media focus on movie stars and other sports stars. Tara cashed in as much as she probably could after the 1998 Olympics. Even then, her celebrity waned pretty fast. She's had a bit of a resurgence lately, but I'll be shocked if it lasts much longer. When I tell my family that Yuna Kim is a huge star in South Korea, they look at me as if I've grown another head. They can't fathom that a figure skater has the celebrity and the endorsements comparable to (or even better than) the sports stars in the United States.