A lot of these shows have attracted some very eminent names in recent seasons. Dominique Morrisseau did the book for Ain't Too Proud. Lynn Nottage is writing MJ, the Michael Jackson musical. Katori Hall cowrote Tina. Colman Domingo had a had in Summer: The Donna Summer Musical. I think these serious playwrights consider these jobs as works made for hire; it's enough to do a slick, professional job and if the show is a hit, they can sit back and enjoy the royalties. The money could finance the writing of many, many plays for Signature Theatre, Playwrights Horizons, et al.