I believe the developers have been working on a new version on EE that includes a GUI. Their development has slowed on new features for EE because of this. It however does not need to be updated as its just controlling other services which it installes through proper repositories allowing them to update themself as needed. Nginx, PHP, mySQL are all installed from their respective repositories. Easy engine does not need an update to use the most current version of its dependencies.
Trellis is very complex to setup and is very different to EasyEngine. Trellis is a platform for separating wordpress sites and having more control and security over multiple sites. EasyEngine is a configuration manager. It controls and maintains the configuration of other programs. Mainly Nginx, PHP, and MySQL. Also Mail and Cache packages.