Google is known for making decisions informed by data, often very large sets of it. That’s a great practice, and one that undoubtedly often leads to some smart moves and happy users. In this case, the Reader team probably saw that a relatively small number of people were using those features, and decided that it was probably safe to kill them off in favor of pushing users toward Google Plus, which is a big, new priority for the company. It’s ironic in a way, because in its big push to reposition itself as a social-friendly company, Google just displaced an entire community of users, effectively shutting down a social ecosystem that had existed for years.
I think this zeroes in on the problem: Google is saying to social-minded Reader users, “We’re going to kill the social network we’ve been freely providing for you. Please use this other social network we’re now freely providing for you. Because of course there’s no way we’ll ever kill that one.” User = Charlie Brown, Google = Lucy, Google’s services = the football. I’ve seen how that turns out.