There's misinformation floating around about Mastodon. Clarifying things:

1. Mastodon doesn't rely on volunteers. It's a registered non-profit that employs people. Kind of like how Wikipedia and Mozilla are non-profits that employs people.
2. Many instances are run by volunteers but not all.
3. Mastodon is just one part of the Fediverse. Benefits of decentralization is that anyone can build on open protocols.
4. Mastodon is big, but Flickr and Tumbler are bigger -- they're joining the Fediverse