It is difficult to provide a totalizing answer here. There are so many reasons why specific individuals become lionized by history and others marginalized by it. If we were to look at Frances Perkins, herself, one could see that her own private and distant demeanor did not enable her to win over the public to recognize her significant role in the New Deal.
A very guarded individual, Perkins guarded her privacy. She preferred to stay in the office at Washington and use her role as Cabinet leader to focus on initiatives that would help the nation emerge from the grips of a depression. Perkins was a champion of labor, but her own background made it difficult for her to use charisma in making her seem "like everyone else." Unlike Roosevelt, who was able to conceal his aristocratic background in being perceived "like everyone else," Perkins was not as able or willing to advocate her own brand in the midst of the suffering and need for governmental action to end the Great Depression. This might be one reason why she is overlooked.
Naturally, another reason that has to be included is the fact that she was a woman in a setting where men occupied most of the power. Perkins had such a difficult task at hand. She had to come up with plans to help pull a nation out of an economic crisis, the likes of which had never been seen before. Add to this that she was being judged for being the first woman cabinet member, and it becomes clear that that she might have simply not been able to conceive of fighting for an increased role of authorship in the New Deal. She was already fighting a great deal.
Perkins represents some of the most important women, giants who laid the groundwork for the improved condition of gender equality in America today. In her role as being a giant, she props the modern generation up so they can ascend even more. This creates the propensity for history to overlook her. Yet, Perkins' role in American History can never be forgotten by a serious student of scholarship.