Because it's not as if she'd never been asked.
After "The Cosby Show," "I was bombarded with a lot of invitations to become the mother on some other 30-minute projects," Rashad said, laughing, during an interview earlier this month at the Television Critics Association's winter meetings in Pasadena, Calif.
"But having worked with Mr. Cosby, having done the best of what there is - and I say is - I couldn't do that. I just couldn't do that. It's not something that I wanted to do. Unless it was of that quality, and that tier," she said.
In the meantime, Rashad, who co-starred with her daughter, Condola Rashad, in Lifetime's 2012 adaptation of "Steel Magnolias," found plenty to do in film and in theater, winning a 2004 Tony for her performance in "A Raisin in the Sun," a play she's since directed, both in Los Angeles and, this past fall, at the Westport (Conn.) Country Playhouse, commuting from Philadelphia for rehearsals.
"I wasn't thinking of returning to television . . . but when I read [David Schulner's script for 'Do No Harm'], that pilot script was so well-written, I thought, not only can I do this, I want to do this," Rashad said.
What she learned working with Cosby, she said, is "that the writing is essential. And I know that from theater, too. The literature in theater is totally different from the literature in film and television. So when you find a script that has that quality of literature [you say] 'Yes, I'll do this.' "
In "Do No Harm," Rashad plays Dr. Vanessa Young, head of neurosurgery at Independence Memorial Hospital (much of which is located inside the School District of Philadelphia's 440 N. Broad St. headquarters).
"It was pretty exciting to get to work that first day and see Mrs. Huxtable," said Pasquale.
"She's smart, she's savvy, she's no-nonsense," said Rashad of her character, adding that as the season unfolds, viewers will see that Young is less in control of her personal life than she is of her professional one, something that couldn't be said of Clair Huxtable, lawyer and ultracompetent mother of five.
(Though it could be argued that the failure to notice that one of your key employees has an entirely separate identity 12 hours a day suggests a problem at the office, too.)
Control's something Rashad's learned a bit about in recent years, as she's expanded her career to become a director.
Seven or eight years ago, she said, "Constanza Romero, August Wilson's widow, she called to say that the Seattle Repertory Theater was going to have a production of 'Gem of the Ocean.' And she asked me to direct it. I had never directed anything. And she said, 'I know you can do this.' And so I did."
She'd never considered directing up to that point, she said, but remembered that while she was an understudy in "The Wiz" in the early '80s, director Geoffrey Holder said to us, 'Every dancer should think in terms of becoming a choreographer. Every choreographer should think in terms of becoming a director. Every actor should think in terms of becoming a director. And every director should think in terms of becoming a producer.' He was giving us permission, telling us it was necessary to think expansively, and to expand one's horizons. Now that was a seed that was planted."
Acting, Rashad said, has allowed her to work with "people that I'd admired, sometimes, from college days and before, never even imagining that I would meet them," including "Mr. Cosby, Sidney Poitier, James Earl Jones, Diahann Carroll . . . Angela Lansbury."
Mr. Cosby? The actors who worked with him as children still call him that in interviews, but Rashad?
"We adore him," she said. "When we're together, and I'm with his family, I can call him Bill. But when I talk about him, I have to give that respect. I have to do that. Because that's who he is. He's so large."
She doesn't see him as much "as I'd like to," Rashad said. "But I hear from him. He'll call me up to tell me a joke."
She's not sure if he knows she's been working in his hometown. (Production on the show's season finale wraps up this week.)
"Surely he must know. The porters in the station tell me, 'He came through here the other day.' We're kind of missing each other like ships in the night. But we'll catch up. We'll catch up sometime."
On Twitter: @elgray