There are primarily two reasons for this — both of which are based on the limited literacy skills of the uneducated masses:
They can’t really comprehend what the fine print means;
They can’t seem to learn from history.
In the Twentieth Century, educated elites — the 1% — learned how to manipulate the masses by duping them with “Free Lunch” offers. The ironic result is that those societies which are based on relatively naive masses are becoming increasingly prone to “falling for” marketing tricks that result in increasingly corrupt organizations. Widespread lobbying is one good example of this grotesque outgrowth, leading to a phenomenon of “you get the results that you deserve” (cf. the movie “Idiocracy”).
This phenomenon is actually a vicious cycle, as the marketing tricks primarily appeal to the uneducated (as described above), and therefore promoting widespread education is shunned, because that would make it more difficult to dupe the masses with propaganda. This is probably the main reason why it took several centuries after the invention of the printing press for public schools to be established across Europe.
Perhaps one good way out of this vicious cycle is to make it clear to people that every time they are offered a “special deal“, they are actually being duped. Indeed, often the people who fall for such tricks themselves think they are indeed getting a free lunch (or at least a “good offer”), so their motivation is actually to get ahead by taking advantage of such “offers“. Once they realize how dishonest and unfair these tactics are, they will presumably be less prone to fall for these marketing tricks.