Ubuntu 18.04 (Bionic Beaver) LTS version ships with PHP 7.2
Ubuntu is the world's most popular Linux distribution. The Operating System is being used by millions of developers for software development on the desktop. It is also a popular operating system for hosting HTTP servers and other service daemons.
Similar to Symfony, Ubuntu follows a predictable release and support cycle. The Ubuntu project releases two versions every year, in April and October. Every two years the April release is slated as a Long Term Support (LTS) release. This release is most commonly used for servers as it will receive security patches for several years.
This cycle makes maintenance of desktop and server installs of Ubuntu predictable. The downside is that the major versions are locked to what they were at the time of the release. In software two years can be an eternity. The current PHP version in Ubuntu LTS (16.04) is PHP 7.0, which is certainly quite long in the tooth by now.
The next Ubuntu 18.04 LTS is to be released in April 2018. This is a great release for PHP developers as it ships with the latest PHP version by default. PHP 7.2 was released in November 2017 and comes with new features and performance improvements. Ubuntu 18.04 will be around and supported well into the 2020's.
Defaults will be defaulting - just deal with it
The Ubuntu and PHP release cycles are now in good sync as PHP releases happen in late of the year, and Ubuntu releases in April. This gives the Ubuntu team ample time to include the latest PHP version available at the time of the LTS release. This has been the case since Ubuntu 16.04 LTS (Xenial Xerus) shipped with PHP 7.0.
Nowadays the exact versions of software packages no longer matter as much as they did when the PHP community was making the (painful) transition from PHP4 to PHP5. It's common to use repositories like the superb deb.sury.org from Ondřej Surý to install latest versions of PHP and Nginx, but not everyone walks the extra mile.
Docker is another technology that has revolutionized the version scene. Ops can now ship complete images including the exact versions of required software. This is made trivial by the fact that the PHP project provides official Docker images. PaaS products like Platform.sh also abstract the versioning nicely, making it a non-issue in hosting.
While the default versions for PHP in Linux distros like Debian, Fedora, Redhat and Ubuntu no longer matter as much, they still do set the lowest common denominator for the mainstreamI think it's important to value defaults, even if you "know better".
P.S. Big hand to my man Nathan for reminding me that the Beaver is rolling in soon.