Reminders: prevent app quit on CMD+W

I'm used to closing only the open windows when pressing CMD+W. However, when all Reminders windows are closed, the application itself quits.

How to prevent this behavior?

This is a long-standing fundamental behaviour in MacOS. From the 2008 Human Interface Guidelines (Chapter 14):

In most cases, applications that are not document-based should quit when the main window is closed. For Example, System Preferences quits if the user closes the window. If an application continues to perform some function when the main window is closed, however, it may be appropriate to leave it running when the main window is closed.

(However, Apple has been ignoring its own guidelines over recent years and changing them to incorporate touch-screen interface design. Notes does not quit on close, and I can't see any residual function.)

There is no way of changing the design of these apps.

Given the speed with which these apps load, and their small memory footprint, I'd just try to think of them as either 'on' or 'off', with Close and Quit doing the same thing.