(I am focusing on the U.S; but posts about other countries are nice.)
Feminism is a social movement that got popular in the previous century; it is a movement that promotes gender equality?
Racial egalitarianism also got popular in the previous century; people were fed up with racial discrimination.
I think egalitarian movements could have easily became popular during this time; egalitarianism promotes the idea that all humans are equal, which is what most civil rights movements focused on; so how did explicitly-stated egalitarian movements manage to not get popular?
They have been and are popular, but such movements are diametrically opposed to the current western world order (imperialist capitalism). There can be no equality under capitalism. The capitalist class, the people who own almost everything and control almost everything, provoke and inflame differences between working people, so that we spend time and energy fighting amongst each other for scraps instead of going after the causes and perpetrators of inequality.
The movements for worker’s rights, women’s rights, and racial civil rights, etc, were all egalitarian movements, and they included far more people than we’re taught today. The history we usually learn about those movements is highly sanitized to remove the revolutionary and class struggle character from those lessons. The capitalists can’t allow us workers to know that by organizing together we can have the egalitarian world some of us dream of.
I guess it’s easier to rally around a specific facet of it with identifiable victims. Obviously progressive people agree with some form of the idea, even if it’s not how the messaging is done.