Sometimes open source code drops off the Net, never to be seen in public again.
Other times, it is published only as a series of release snapshots, with no publicly-accessible version control repository.
The Conservatory exists to address both situations.
Welcome to the Conservatory:
The Conservatory is an archive for open source and public domain code that doesn't have any other clear canonical version-controlled home on the public Internet. It's a place to preserve a convenient version history for code whose authors
Don't keep it under public version control, or...
Have abandoned it, neglecting even to keep a copy on a public server, or even...
Have actively tried to remove it from the Net, open source license notwithstanding.
You might think that (3) never happens, but actually an instance of it was part of what motivated the creation of the Conservatory... and then it happened again.
The Conservatory is strictly about preservation and ease of revival. The presence of a repository in the Conservatory is not a criticism of that code's authors or former maintainers. No one is obligated to maintain a public repository of anything, unless they've signed a contract to do so, in which case their obligation is to the contractual counterparty not to the public at large.
Update 2019-11-14: Software Heritage and the GitHub Archive Program do something similar to this, but it's not clear whether ease of revival is as high a priority for them as it is for us.
The Conservatory is archival. Repositories here do not take pull requests because they are not meant to be the "social master" repository of their respective projects. If you want to work on one of the codebases, please fork it to a new repository and work on it there. If the code still has an upstream maintainer, you can work out with her what relationship your fork should have to her upstream releases. If there is no upstream maintainer, then maybe your fork will catch on and become the new master — and the Conservatory's copy will become less and less important (as well as increasingly out-of-date), which is fine.