Perhaps (and strictly speculating here) these numbers are due not to the star power of the performers, but to the public unfamiliarity with these plays?
Bradley Cooper in The Elephant Man- big star AND recognizable story.
James Earl Jones and Angela Lansbury in Driving Miss Daisy- big stars AND popular play.
I think, no matter how "big" a Hollywood star is, you need both elements to bottle an audience...
https://newplayexchange.org/users/99643/amanda-delalla