Many symposia and special journal issues over the last several decades have been devoted to concerns about the decline of philosophy in teacher education programs. I pursued an answer for my doctoral project and found institutional explanations are rarely invoked in the "decline literature." I have sketched here the theory and have shown it to be equally applicable to the last several decades of this literature. I argue that institutional organizational theory (IOT) shows how teacher education institutions have changed over time in a way that has ultimately rendered the environment less and less hospitable to philosophy of education curriculum and faculty. Particular attention is paid to the educational context of Ontario, Canada, but I also include the wider American and British decline literature. In the final pages, I offer de-institutionalizing solutions that, if realized, could provide a new soil in which philosophy and other educational humanities fields could take root again in teacher preparation programs.