Farrah was at the peak of her fame while she was on CHARLIE'S ANGELS. As her manager from that time remembers it, the show was "always trying to keep up" with Farrah because her celebrity was outreaching that of the show. Indeed, it was Farrah whose name dominated the popularity polls, and who was usually mentioned first when magazines or tabloids mentioned the show. I recall seeing the video from where CHARLIE'S ANGELS won an Emmy award in early 1977. Farrah Fawcett-Majors (as she was known at the time) was the very first name mentioned.
In saying all that, Farrah really upset some powerful people in the industry when she walked out on the show after the first season. No, she had not signed her contract because they hit a wall with merchandising, but she had verbally agreed to stick with the show. And when she decided to walk, it ruffled some feathers. So, as I understand it, she was gray-listed in the industry. Apparently, at a screening of John Travolta's SATURDAY NIGHT FEVER in 1977, the audience booed when the camera panned over and stopped on Farrah's famous red swimsuit poster. Her fans were upset with her, too, not just the producers and "suits" in Hollywood. She also apparently missed out on a movie deal with MGM that the CHARLIE'S ANGELS producers had set-up for her.
So, as it goes, people were angry with her and therefore they didn't hire her. What movie and TV projects she did do weren't well-received because they were of a lesser-quality.