Don't know how they decide which package could get update in this way.
Most packages in Raspbian come from Debian from which it is derived. When Debian updates a package that eventually finds it's way into Raspbian. Packages get updated by their package maintainers who are generally volunteers. The maintainers build the package and test it before it goes into use. So it's understandable that the packages in Debian/Raspbian can lag behind the latest versions.
PHP is quite like Node.js, I think.
Only if you have only glanced sideways at some source for less than a minute.
Apart from both being interpreted language systems with some superficial C like syntax, they are vastly different. Built for different purposes. One can do a lot more, more easily, with node.js than PHP.
I believe Web is changing(advancing) too fast these days, reinventing too much wheels.
Moving from PHP 7.0 to 7.2 or updating node.js is not so much reinventing the wheels as polishing the old ones.