The problem is not lack of 7.2 support.
The issue is that people unsafely decides to go self-hosted without knowing what they are getting into.
Often, this leads to hacking and slashing several tutorials together (as it seems your example was doing), often leads to broken unmanageable environments, with several 3rd party repositories that conflicts each other.
Consider:
Ubuntu 18.04 uses 7.2,
but
Centos Stretch still comes with php 5.4,
(forcing you to go trough a similar process to install 7.1)
Debian seems to come with php 7.0,
(needing the same amount of commands to install 7.1 (If you want) as both ubuntu and Centos)
No-matter what distro you decide to use, if you don't know what you are doing, or at the very least, follow just one specific tutorial, things will at some point provide problems.
