Abstract Digital governance is a public concern, yet under private control. After numerous scandals, all stakeholders in the European Union (EU) agreed to establish a “novel constitution for the internet” that would effectively constrain the power of large platforms. Yet the Digital Services Act (DSA) ultimately legitimized and institutionalized their position as the gatekeepers of the internet. Why? We argue that platforms prevailed thanks to their ability as intermediaries to quietly shape the available policy options. Our “platform power mechanism” combines institutional and ideational sources of business power to show how big tech drew on its entrenched position as an indispensable provider of essential services and promulgated the idea of itself as a responsible and neutral intermediary. We follow the unfolding of platform power through a process-tracing analysis of Google and Meta’s activities with respect to DSA legislation from its announcement (2020) to its adoption (2022). Besides contributing a reconceptualization of the DSA as a regulatory capture, we integrate the notion of platform power into a “regulator–intermediary–target” model and demonstrate how gatekeepers have exploited information asymmetries to share “the public space.” Our analysis thus supplements established approaches that have derived regulators’ deference to platforms from the tacit allegiance of consumers.