I'm sure there were many reasons it died, but my theory is that Google strategically wanted to kill it because the User was in control of the data-sources and the algorithm. Google wanted people to migrate to Google+, News, etc. where they control what you see.
This is what Facebook and Twitter did. Their feeds used to be a simple chrono sort of sources you determined, but then they slowly took control.
In my mind, all these companies have shifted from being Platforms to being Publishers. While they aren't writing the content, they are actively choosing what content you see and don't see, i.e. being the Editor.
I think this might be right, but this could be because it was an thus an awful interface for anyone who wasn't somewhat along the HN-user spectrum of technical nous.
So maybe Google did the world a favour by binning Reader.
I used Feedly for a while, but I pretty much abandoned my RSS fix after the demise of Reader.
Maybe killing Reader was a means to an ends.
Nowadays you are supposed follow the Internet randomly, based on whatever you happen to see in social media by chance or curated by algorithms. It’s not a good way to get a balanced view.
I have been using https://elytra.app recently. Pretty happy so far (iOS only at the moment, but the developer is working on a web version)