When Dallas began, Victoria Principal (https://en.wikipedia.org/wiki/Pam_Ewing) was the main lead. But then it gradually re-focused (https://www.imdb.com/title/tt0077000/trivia) into Larry Hagman and Patrick Duffy's show. Principal's character (https://tvtropes.org/pmwiki/pmwiki.php/Characters/Dallas) went from being lead to merely supporting, to dead.

Aside from the cancer arc which gave her the Emmy, wasn't Barbara Bel Geddes really inconsequential on the show in the greater shape of things as Miss Ellie (https://en.wikipedia.org/wiki/Miss_Ellie_Ewing)?

Susan Howard meanwhile, got fired because she didn't agree with her character (https://en.wikipedia.org/wiki/Donna_Culver_Krebbs) getting an abortion.

And Priscilla Presley (https://en.wikipedia.org/wiki/Jenna_Wade) was well....Priscila Presley (http://tellytalk.net/threads/the-introduction-of-priscilla-presley.715/).

It seemed like Linda Gray (https://en.wikipedia.org/wiki/Sue_Ellen_Ewing) was ultimately, the only female in the cast who had a good arc and she wasn't even a regular when the show started.

Dallas was a male-dominated show and the producers, especially Leonard Katzman, were mens men. I don't think they were interested in progressive story lines for the "womenfolk."

I'm not saying this based on any facts, just speculation.