Two factors are at work here; first, in a capitalist society (or modern mixed economies, which retain this feature of capitalism) visibility is driven in large part by class and wealth, so higher-status individuals will appear more significant (especially from outside the movement) simply because of their status.

Second, the modern popular concept in the West of the "middle class" is almost entirely part of what socialists (and others following the classical analysis of class in capitalist societies) call the working class (the traditional capitalist-economy middle class, the petit-bourgeoisie, aligns better with the current popular concept of the"upper middle class" and lower range of the upper class.)

In modern Western parlance, "middle class" is the middle income segment of the wage-labor dependent segment of society; in traditional (socialist in origin, since they first described and analyzed capitalism) the wage-labor dependent segment is the working class.

And, yes, the segment of the working class that is able to afford to spend effort directed beyond immediate survival, and with the most to lose, is usually the base of most reform efforts and resvolutions (socialist or otherwise), and usually the petit-bourgeoisie is significantly involved, too (though also significantly involved in defending the status quo), since very early in the capitalist (and pre-capitalist transitional) world.