Why do apps stop supporting older Android versions after some time? My mother had a shopping app on her old smartphone which runs Android v6. Recently I noticed that the app on her phone was no longer supported. I've seen such things happen on old phones generally with many apps. I just wanted to know, why do companies drop their support to older OS versions after few years? Does it cost them a lot to continue the support to older OS versions as well? Does it require a whole team to be hired to just keep managing the support for older OS? Just being curious about this. Thanks.
There are two ways to support old Android versions:

Build one app that makes use of compatibility patches to supports old Android versions (down to a specific version) but also support all modern Android versions.

Build two or more apps each for a set of Android versions.


The second option is of course very costly as you have to develop maintain each app app version independently (or at least large parts of the app). This way is often not used or only if the app has been completely rewritten for new devices and for old devices the old version remains with minimal to no support.
Therefore the common way is option 1 – one app that has all compatibility fixes included. The main problem is that newer Android versions include interesting new features that are not (fully) available using the compatibility system Google provides. Therefore if you want to make use of them and the functionality is not optional in your app, app developers may decide to drop support of older Android versions in favor if being able to use new features of new Android versions. Decreasing the number of supported Android versions simplifies the app as old workarounds can be removed and don't have to be maintained anymore. And of course it removes the necessity to test the app on such old devices which can be a problem if you want to test your app on physical devices (not emulators) as old devices break and are more and more difficult to get.