my initial thoughts:
many people know there is something major wrong with the world that humanity has created. many people, when faced with such a realization, ultimately either choose to accept it and "make the best of it", or they decide to try to "change the world". when "changing the world" is one's goal, the only pragmatic approach seems to be to jump on some bandwagon of "reform" (or start one of your own, and try to find as many adherents as possible). one can find many who agree with some elements of a reformist platform, and so one does not feel so helpless and isolated in their ideas. they can feel like perhaps they actually ARE changing the world, when they successfully lobby for a new law, or get their favorite "minority" elected to the white house, or convince whole foods to support unions, or whatever-the-fuck.
of course, i find this largely delusional.
to dig one layer deeper, i think a huge part of why the above is the norm, is that so few people can imagine meaningful change that does not apply to "society" at large. it is difficult to imagine anything more substantial than minor reforms when your target is that huge. however, it is quite easy to envision fairly radical changes when the target is "my life and my relationships".
i was an activist for many years, and even the "victories" (few and far between) were shallow, unsatisfying (beyond the initial moments of celebration) and practically speaking ... not even a blip on the radar of the status quo. i realized, eventually, that my hope/expectation of changing the world was not only unrealistic and unhealthy, but it actually did NOTHING to further my own freedom.
i think people (those who might want more dramatic change) are reformist because that is the only way they can envision change happening, in the context they perceive. i wish more of them would re-think their context.