Forest conservation policies could potentially become a centerpiece for climate change mitigation. Incentive-based conservation policies, such as payments for environmental services (PES), are seen as promising approaches to reduce deforestation. Yet, arguably the adoption of upscaled PES programs has remained slow, and when implemented their design often diverges from the principles laid out in the theory-based PES literature. In this article, we concentrate on some political economy forces that could help explaining the gap between PES theory and practice, with respect to policy adoption, including opportunities and challenges in this process. Public policy theories grasp the adoption determinants of three large, government-led incentive programs for forest conservation in the Amazon, in Peru, Ecuador, and Brazil. We use Kingdon's Multiple Streams Framework to analyze decision-making regarding program initiation, including key stakeholder interviews, to understand policy choices. We find that environmental concerns are not always the prime motives for PES programs, as political and institutional contexts limit environmental policy-makers' actions. Yet, policy choice processes become less constrained when environmental issues are closer to a government's priorities.