This study examines the co-evolution of tourism and the administration of Finnish protected areas (PAs), specifically focusing on how administrative legitimacy-seeking influences sustainable tourism governance. Drawing on concepts from new institutional theory, namely isomorphism (organizational convergence), legitimacy-seeking (the pursuit of societal approval), and decoupling (the separation of formal structures from practices), we analyse key policy documents and annual reports from Finnish Parks and Wildlife from 2005 to 2018. The findings of our study reveal a dual shift in PA governance: 'platformisation,' where PAs are transformed into state-orchestrated platforms that facilitate the creation of value and legitimacy through the growth of tourism, and 'corporatization,' where private sector governance logics are adopted within public administration. These shifts redefine the state's role in commercializing nature, emphasizing economic outputs and regional development mediated by tourism. We observe a decoupling of organizational practices between broader environmental policies and tourism development objectives, driven by the pursuit of legitimacy. Overall, this research contributes to the critical discourse on the evolution of PA governance. It highlights the significance of understanding these institutional constraints in the context of sustainable tourism governance and evaluates the wider environmental policy implications of tourism growth.