Excerpt:
Most major subreddits show a decrease of between 50 and 90 percent in average daily posts and comments, when compared to a year ago. This suggests the problem is way fewer users, not the same number of users browsing less. The huge and universal dropoff also suggests that people left, either because of the changes or the protests, and they aren’t coming back.
It is probably that those who used third party apps were those more likely to try to get karma and engage with the site. The switch wasn’t worth it for the heavy users making posts, so posts fell.