How do you "know" this? Show some proof! RSS has two well-known use cases: news and podcasts. It is fighting a pitched battle against players with deep pockets who want you to consume content where they can monetize it with ads.
Google Reader survived for as long as it did because such a service is incredibly cheap to run. Google only ended it to push people to Google+. Many of the various competing providers that popped up during that period are still around, but I would not say it is flourishing.
This is what Google thinks of RSS:
https://trends.google.com/trends/explore?date=all&geo=US&q=R...
Note a rise and plateau centered around 2005 and a brief peak in 2013 (when Google killed Reeder).