Infrastructure providers have a monopoly or an oligarchy over a geographic area and do not know what specific activities users engage in online, aside from which websites are visited.
Application providers can build their monopolies based on network effects and potential competition is not constrained by an external limitation, like geography. They know what users do on their platforms.
DMCA treats them the same. Cutting off someone’s Internet access seems like a very early 00’s solution to piracy, when you could still conceivably walk into a business and fill out a paper job application. Legal concepts need to evolve with the Internet and we need finer grained distinctions.