IntelliJ IDEA - Maven home directory setting resets for new projects

IntelliJ IDEA 2018.x or later:

Older versions:

You can change it in the Template Project Settings so that all the new projects inherit this setting. You can access it from the File menu when the project is open or from the Welcome Screen: Configure | Template Project | Settings.

Intellij 2018.2 its now under File > Other Settings > Preference for New Projects

In IntelliJ 2020.2 it's now directly

File -> New Projects Settings -> Settings for New Projects...

In Intellij 2018.1:

File -> Other Settings -> Default Settings...

Changing default settings will apply only to new projects.
Current project won't be affected.