Anyone who makes use of patented technology that has not been licensed by someone upstream can, indeed be sued, at least in principle. Consider the case of Innovatio, who tried to go after businesses who were providing WiFi for their customers by using routers that contained chips that contained potentially infringing circuitry. https://www.eff.org/deeplinks/2014/02/infamous-wi-fi-patent-... . The reason we don’t see more suits of end customers is that it’s not economically feasible - nobody would sue millions of consumers to collect $.10 each, when they can sue the upstream manufacturer just once and collect hundreds of thousands or millions of dollars in royalties.