The view count sharply dropping off around 2013 mirrors (to me) the increasingly more narrowly defined scope of the site's acceptable content than what it was when it started.
Digging through my local notes and journals as to why I stopped, I have an unpublished draft blog post from 2012 that has some examples of bad questions from 2012, and I later added https://meta.stackoverflow.com/questions/252506 to it as something that resonated with me - "Why did I even help this guy? I have just been wasting my time". I must have been burned out on the whole thing by that point, but it was 10+ years ago and I've not even visited SO in years.
I do remember they added a tier of moderation around this time, and I had sufficient points to have access to that. Every time I visited the site it showed a red dot on the stuff-to-do icon, encouraging me to review a queue of bad questions. I'm pretty sure that was when I decided to stop contributing, because the site felt like it was more focused on the tedious bureaucracy of it all than the technical stuff.
One of them changed so that when you reviewed something it would show you at random a sample that had already been reviewed, but this was not indicated in any way. If you got the review "correct" it said "well done, that was to test you are paying attention!" - it was even more patronizing if you got it wrong.
I was so annoyed that they had wasted my time in this way that I stopped contributing all together. It was a wake up call that the whole site was taking advantage of our free labor, and I decided to do better things with my time.