Why an older version of an app STOPS working when a new version is available?

I have a Samsung Phone (AT&T) and Samsung Tablet. When a new version of an app is made available, both systems prompt me to install them. If I don't, the existing app versions on my devices STOP Working!!! WHY??? Is this to force people to download the new versions? The new versions want access to everything on the phone which is ridiculous. Even Microsoft lets you decide what to update and keeps your older version running. The never-ending updates only serve to load better spyware or siphonware on our devices and force us to upgrade as our devices become bloated and slowed down with updates (more money for companies & Google). In the meantime, the end user is being screwed.

I need to have the apps on my devices to continue to work regardless of the existence of the updates!!! That's why I bought the devices in the first place, and this Google/Samsung/AT&T practice is bordering on extortion!!!

Welcome to Android Central! Can you give some examples of apps that are no longer working because you didn't update? In my experience, that kind of behavior is very rare. Most apps will continue to function normally without updating for quite some time. But at some point, the app may have such a major update that previous versions will no longer be supported. That's normal for any kind of software--there are plenty of examples of Windows programs whose obsolete versions are no longer supported by the developer, and don't run on modern versions of Windows.