I never heard a reason (whether it was her decision or theirs). Groff didn't go either: the original reason was stated to be previous commitments (and he is appearing in another play) but Riedel speculated that he turned them down over money, because they were only offering "scale".
I'm sure someone else will be able to enlighten us further.
If we're not having fun, then why are we doing it?
These are DISCUSSION boards, not mutual admiration boards. Discussion only occurs when we are willing to hear what others are thinking, regardless of whether it is alignment to our own thoughts.