Previously, Windows apps that wanted have simple, persistent configuration/state variables would either have to roll their own config file buried in a subfolder somewhere or resort to putting them in the global Environment Variables.
The Windows Registry was massively better because it was centralized, hierarchical and allowed hundreds of apps to store thousands of settings in an organized way.
What you should really be asking is: What happened to the content-addressable hierarchical, distributed and object-oriented file store that was supposed replace the DOS file system we're still (basically) using today?
Google is your friend.