We don't know why they didn't present them. That's the thing.
One option is that she had her defence team made very bad decisions or they were inadequate.
Another is that it was difficult to get experts because they were nervous about the consequences for their reputation. If that's the case then there are serious issues with the fairness of the trial.
Then of course there are those who say that they didn't bring any experts because there was none who could help her or they wouldn't have stood up to scrutiny. but we don't know if that's the case.
The defence didn't try to bring any evidence from Dr Shoo Lee during the trial, why? We don't know
For the appeal they tried to get some evidence from him brought in, but it doesn't sound like it was nearly as in-depth as it should have been. Why? We don't know. Did the defence just not ask him to review the babies medical files? Or did he say he wouldn't? We don't know.