“Most readers read these magazines on Shabbos and (if I understand the halacha correctly) it is prohibited from anyone to read or look at advertisements on Shabbos…”
What marketing study or credible evidence is there that “most readers” read these newspapers or magazines only on Shabbos?? If we extend your logic, it would be assur to sell many products which are muktzah or whose use might be assur on Shabbos. For example, a frum yid might have the time on Shabbos to use his/her cellphone (even a kosher phone) to call mishpacha or friends to just schmooze, something they might not have time to do during the week. Should we ban the sale of kosher cellphones because some ehrliche yid might call his shver on Shabbos?