As stake holders they also all need to be contacted for any issues that may come up. This was shown with the recent re-licensing of parts of VLC, https://lwn.net/Articles/525718/. The linux kernel would also has a similar problem, since there is no copyright assignment, all contributors would have to agree for anything like a license change.
Allowing for a non-profit to hold the full copyright is also useful, as individual people may come and go, change opinions. For GPL software, Giving copyright to the FSF also protects against changes to non-free licenses. Having the guarantee that the software will stay opensource is something that agrees strongly with RMS's views.