It would be a crazy antitrust violation for all of these companies to work together on something closed source - e.g. if Facebook/Google/Microsoft all worked on some software project and then kept it for themselves. By hosting it at a neutral party with membership barriers but no technical barriers (you need to pay to sit on the governing board, but you don't need to pay to use the technology), you can have collaboration without FTC concerns. Makes a ton of sense and really is a great way to keep tech open.