Conjectures have gone both ways. That Frank Carroll wanted to work the triple Lutz/triple loop into Michelle routine and it wasn't working from Michelle's point of view. And the opposite, that Michelle was the one pushing for tougher content, while Frank was the one saying, if it's not broke don't fix it.
At 2001 Skate America Michelle missed her 3T/3T. The next week at Skate Canada, having announced the split with her coach, she fell on the first jump of her 3T/3T and tried a 3Lz/3L but was unsuccessful. She finished third for the first time in years. A few weeks before that was the famous press conference in which they asked Michelle and Frank how training was going. Frank said, everything is going fine. Michelle, almost in tears, burst out, no, nothing is going fine!
To me it seems likely that team Michelle was working on the 3Lz/3L that fall but had not developed the 80-90% consistency that Frank required before putting it in a program.
I don't think that was the cause of the breakup of the team, though. I think Michelle was just going through that period in a young person's life when the burden of the world seems crushing, when you are torn between independence and relying on the advice of parents and teachers, when every decision you make seems like the wrong one. Michelle was afraid of losing out on a normal life, but also wanted her special life. She wanted to go to college and to live in the dorm like everyone else -- but then again, she didn't.
The only thing Michelle ever said about why she split with her choreographer and coach was, "I want to take control of my own skating."
Substitute "life" for "skating," and I think that is as close as we will ever come to getting inside Michelle's head.