Jared presented a good broad categorization of open ed motivations (Philanthropic, Strategic, Pedagogic, Economic) and I liked the framework Michael proposed as well; motivations based on values and motivations based on value. Picking up from there, here's a little analysis on the "whys" (at least the public ones) of some top open education initiatives...
MIT OpenCourseWare : Unlocking knowledge, Empowering minds. "MIT OpenCourseWare is an idea - and an ideal - developed by the MIT faculty who share the Institute's mission to advance knowledge and educate students in science, technology, and other areas of scholarship to best serve the world."
Values: excellence in instruction, universal access to information, education for service Value: PR and reputation effects for the institution, competitive advantage, indirect sales (support recruiting)
OER Commons : Free-to-use Teaching and Learning Content from Around the World "expand educational opportunities by increasing access to high-quality Open Educational Resources (OER), and facilitating the creation, use, and re-use of OER, for instructors, students, and self-learners.
Values: improved OERs, improved instruction, improved access, multi-culturalism Value:
C()SL at Utah State : Open and Sustainable Learning "is dedicated to increasing access to educational opportunity worldwide...we believe that all humans beings are endowed with a capacity to learn, improve, and progress. Educational opportunity is the mechanism by which we fulfill that capacity. Therefore, free and open access to educational opportunity is a basic human right."
Values: rights-based access, humanism, education for service, advocacy Value: PR and reputation effects for the institution
Commonwealth of Learning : Learning for Development "helping developing nations improve access to quality education and training"
Values: humanitarianism/charity, access Value: PR and reputation effects for the institution
Carnegie Mellon OLI : Working to help the World Wide Web make good on its promise "Using intelligent tutoring systems, virtual laboratories, simulations, and frequent opportunities for assessment and feedback, OLI builds courses that are intended to enact instruction – or, more precisely, to enact the kind of dynamic, flexible, and responsive instruction that fosters learning.
Values: innovation, relevance/effectiveness/flexibility in learning Value: PR and reputation effects for the institution, research platform, technology integration/exploration
WikiEducator : Free elearning content. Just try it! Our community will support you. "The WikiEducator is an evolving community intended for the collaborative planning of education projects linked with the development of free content; development of free content on Wikieducator for e-learning; work on building open education resources (OERs) on how to create OERs. networking on funding proposals developed as free content."
Values: community organizing, improved OERs Value: cost-savings for participants