Since the people behind and maintaining the plugins <= 1.5 were forced to rename the software project into Monitoring Plugins there was some work behind the scenes and much QA work necessary to release the software in a proper state. This happened 4 weeks ago with the release of the version 2.0 of the Monitoring Plugins.
With one day of delay the package was uploaded into unstable, but did hit the Debian NEW queue due the changed package name(s). Now we (and maybe you) are waiting to get them reviewed by ftp-master. This will hopefully happen before the jessie freeze.