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.
You have to remember that APIs were used massively by third party apps users.
I don't see a reason to attribute the API related drop more to automation than users stopping browsing reddit because third party app ban.