There is several how to because everybody has a different view on what to use
There doesn't need to be a single solution for any of these, but having all the setup be manual doesn't help most users. That's why we went with deb/rpm in the first place.
As far as the choices - all of my clients just tell me "make me a mailserver". They don't choose the specs, they tell me the requirements and I choose the specs. Frankly most people don't care why underlies their tools, for better or worse. Of the hundreds or thousands of packages I use, I can say I've only studied the .specs of dozens of them, so at a certain level apparently I don't care either.