The issue may simply be American Actors Equity. It makes sense. Part of their purpose is to protect and keep jobs for American actors in the union.
Concessions and swaps are worked out all the time with British Equity, but I'm guessing there was a deal in advance with Mary Poppins that an American actress would originate the role on Broadway.
That could easily be the case here with Finding Neverland, which would prevent Daniel Evans or Julien Ovenden from originating the Broadway role, especially if they've already made a concessions with Kelly this time. Maybe one of the two leads had to be American, etc. And maybe Kelly now has dual citizenship allowing her to join American Equity.
Who knows?
"Jaws is the Citizen Kane of movies."
blocked: logan2, Diamonds3, Hamilton22