This used to be more of a problem, but the support library deals with this more nowadays. Not for every change and new feature, but for most of them.
Most of the graphical widgets in Android apps come from the support lib.
The most complex and important is probably RecyclerView : it allows to implement recycling lists of items and replace the framework implementation.
It is not even part of the base framework since it is way more convenient to update it independently from the OS (and as a dev, you only have to handle whatever version you ship your app with).
There are shims for many of the framework features too, for exemple notifications or media.
Overall it makes the dev experience very smooth.
IMO the problem with the lack of update is mostly security
https://developer.android.com/guide/topics/media/exoplayer.h...
RecyclerViews are only implemented in the support libraries, even for newer versions of Android. I haven't used Exoplayer personally but by reputation it does all of the hard media stuff for you.