For the most part, unfair as it is, there is an accent on youth and physical desirability in an actress' career that isn't as important in an actor's. If they make wise career decisions, male actors can go on seemingly forever, playing opposite younger and younger actresses...or often not opposite actresses at all, as most screen roles are written for men, with a token female love interest thrown into the mix.
Occasionally there's a hit movie like Steel Magnolias
or The Devil Wears Prada
where the cast is predominantly female, but that's unusual in the broader scheme of things.
Another thing to remember is that while Dunaway was an A-list star, she wasn't necessarily a "people's star". She was a special type, in special, intelligent films. Even her looks (cool, willowy and angular) weren't as approachably embraceable as say, a Jane Fonda or a Jessica Lange.
As the New York Times review for Eyes of Laura Mars
(1978) noted, "Miss Dunaway is perfect for her role, but it's beginning to look like the only role she cares to play. Hysterical jitters, countered by fits of extreme hauteur or assertiveness, have constituted so many of her recent performances that it's hard to remember what else she can do. In any case, high-minded artistic fluttering — the kind Diane Keaton attempts in "Interiors" — comes so naturally to Miss Dunaway that Tommy Lee Jones, as a down-to-earth, soothing cop, is not just a good foil but an indispensable one."
Also, post Oscar, and when Dunaway adopted her son, she squandered a key period by accepting smaller roles that paid very well...The First Deadly Sin
(1980), The Champ
(1979). These weren't even hit movies. Then to make things worse, she moved to England, which even further limited the work she could accept.
Her comeback role was in Barfly
(1987) and she's excellent in it, but by then the ship had sailed for her to stay on top as a major star, in Hollywood terms.
All this was combined, as noted above, with a reputation for being difficult and sometimes unprofessional to work with...as well as carting around a substance abuse problem, to boot. There were simply easier options for producers to pick from, rather than hiring Dunaway.