(By the way, unzip is arguably not feature complete. The ZIP spec has been updated multiple times since 2009, with the notable addition of the Zstandard compression method, among other things https://pkware.cachefly.net/webdocs/casestudies/APPNOTE.TXT)
Per the upstream, https://infozip.sourceforge.net/, "UnZip 6.0 was released on 29 April 2009".
But there are not truly 0 maintainers, because distros maintain their own patchsets, for example: https://git.launchpad.net/ubuntu/+source/unzip/log/
(By the way, unzip is arguably not feature complete. The ZIP spec has been updated multiple times since 2009, with the notable addition of the Zstandard compression method, among other things https://pkware.cachefly.net/webdocs/casestudies/APPNOTE.TXT)