While numerous open source projects operate on their own, others decide to join well-established foundations such as the Apache Software Foundation (ASF) and the Eclipse Foundation. Although many studies have investigated the motivations of individuals and companies contributing to open source, it remains unknown why projects decide to join software foundations. In this paper, we study the motivators behind the projects’ decision to join the ASF, the geographical and organizational characteristics of these projects, and the differences between projects in terms of their motivations. To this aim, we analyzed 292 proposals submitted to ASF, and we found that there is an increasing number of company-based and Asia-based projects joining the ASF in recent years. Furthermore, we found that more than half of the projects are motivated by the desire to foster their community, strengthen the outcome of the project, increase interaction with other communities, and boost technical development. Our work shed some light on projects’ expectations from the ASF. Having this understanding can help foundations to identify ways of supporting newly joined projects, while the prospective joiners can better decide on whether ASF is the right place for them by checking the alignment of their motivations and motivations of projects that have joined in the past.