Each of the familiar themes which used to ship with Moodle releases are now part of the plugin database in advance of them not being available by default to your fresh Moodle install. The themes that have been moved to a repository home rather than installing with any new Moodle include Binarius, Sky High, Nonzero, Nimble, Magazine, Fusion and others (many of which were part of Moodle since the 2.0 release).
The removal of these themes makes way for the inclusion of only two themes with new Moodle installs, Clean and More which are both Bootstrap-based responsive themes. Don’t worry though, themes are easy to add from the Moodle.org site through the plugin administration on your own Moodle install.
Browse the list (museum?) of themes at https://moodle.org/plugins/browse.php?list=category&id=3