* Scheduling conflicts. Actors from the original Broadway cast may not be available to film the movie adaptation due to other commitments. This can be especially true if the movie is filmed several years after the Broadway production closed.
* Creative differences. The director of the movie may have a different vision for the cast than the director of the Broadway production. This can lead to changes in the casting, even if the original Broadway cast is available.
* Budgetary concerns. Movie productions often have stricter budgets than Broadway productions. This can lead to the casting of less expensive actors, even if they are not as well-known or experienced as the original Broadway cast.
In some cases, the movie cast may include some actors from the original Broadway cast but also some new actors. This is often done to accommodate scheduling conflicts or creative differences.