such as why would it have to be concentrated in "one person”?
Because that’s how the existing extended setup was originally built and maintained.
Why the build farm is gone and how hard would it be to put it all back and running?
Probably because the people maintaining it are no longer actively working with pd in their spare time. Setting it a new one involves money, time and maintenance. A sponsoring institution, as Jonathan, has pointed out would really help for those points.
Why does it always have to be one or two versions behind vanilla and not just get the latest vanilla and "extend" it?
It doesn’t have to be that way, but it takes *alot* of work to test things against new updates and changes. Pd extended not only bundled lots of externals but was a test bed for UI updates and other types of modifications to the core that could not be easily updated from the work being done ahead of it in vanilla.
Think of it as editing a book for an author. You get the latest version from him, you make some changes then you get a few other people to help add and move things around and now you have you “community edition of the book”. But, by that time, the original author has already changed a number of other things, some of which may conflict with your changes. So now updating your version with the author’s will take alot more time. This is the main reason why extended was always a little behind. It simply takes work and, unfortunately, Hans was really the only one doing it.
And also, why does it seem to me the pd distros always get concentrated in one or just a handful of people?
It’s open source. It doesn’t have to be that way but it is because it relies on people donating their time for free to do this work. Luckily, some people can do it as part of an institution, but not all.