Thing is, how many consumers actually have all the information, or are willing to take the time to look for it? a "free" market also means perfect information, which obviously never has and never will exist, that's one of the reasons that big corporations have an advantage because they have more means to inform the public on what benefits them as opposed to maybe a smaller company with a better product that can't invest in communication. And no, the internet does not lead to "perfect information".
Add to that the mentality of "I can't change things on my own" (similar to why people have a hard time making eco-friendly changes) and nothing changes. Regular people ain't got time to worry about organizing a boycott or whatever you want to call it, nor to seek out better alternatives. They got jobs, kids, occupations, etc. We all know about child labor in manufacturing our shoes, t-shirts etc, we all are against it (well,probably not "free" marketeers but whatever) but we still buy those same clothes, because we can't be bothered to look for alternatives.