It think you got things very mixed up here.

Google Reader was shut down in 2013.

At that time Facebook was THE hugely dominant social network, with Twitter solidly established, and Instagram rapidly becoming popular.

Google Reader was well past it's prime, most "regular" users had already moved to those platform, outside of the more hardcore Tech circles.

Google Plus was also really struggling,so they probably wanted to push the user base on to their "real" social network.

Yeah, the RSS ecosystem was never the leading ‘social network’ by number of users, but it used to be systemically important, in a way that it isn’t today. Keeping track of what was happening in many fields (particularly tech, but also others) used to be primarily via RSS, now Twitter (and in some cases moving to Mastodon, now).

I never used Reader but I did use another one that also folded, a year or two before Reader went away. Then it got bought and came back, changed, and that stutter interrupted my process and I never really recovered. I set up Feedly and then don’t use it.

I think I’m from the generation(s) that expect to spend a lot of time in a browser window instead of hopping between applications triggered by notifications. So the moment I put something into an app, if it’s not situation dependent like Apple Fitness, or team chat for work, it’s just too much friction to make it a habit.

The most fascinating bit for me is that people actually used any of the social features of Google Reader. I just read my feeds and interacted with nobody, and that wasn't too uncommon in my circles.

Oh, I’m not sure how many people ever used Google Reader’s _own_ social features. But RSS facilitated social networking via blog (remember, for a while ~every blog had comments and trackbacks, on which twitter quote-retweets are based), and, unfortunately, Reader became so synonymous with RSS that its death largely killed that ecosystem. It was really noticeable at the time; blog activity really fell off, and even if you switched to an alternative RSS reader which stayed working (a lot of readers used Reader as a backend!) you had to switch to Twitter to keep up with what was going on.