ServerPilot builds our own "deb" packages of Nginx, Apache, and PHP. We do not install the versions of these provided by Ubuntu.
The first reason we build our own packages is so we can configure your server with the latest, fastest, and most secure versions of these packages.
We also want to ensure that we can provide the same versions of these packages across different versions of Ubuntu. If you are using servers running Ubuntu 16.04 and start using servers running Ubuntu 18.04, we want you to have all of the same versions of Nginx, Apache, and PHP available.
Lastly, in the case of PHP, we also want to provide multiple versions of PHP side-by-side on your server. This is what makes it possible for a single server of yours to run apps with PHP 5.6, PHP 7.0, PHP 7.1, and PHP 7.2.