Looking at that source, there's a pretty straightforward explanation of where the page views come from.

- Last month, Stack Overflow had ~142,575,642 visits.

- Last month, Google gave 127,896,508 visits to Stack Overflow

- Last month, Bing gave 7,491,274 visits to Stack Overflow

You could say that the Stack Overflow # of pageviews depends mainly on:

- How often people are searching Google/Bing for answer.

- How often Google/Bing rank Stack Overflow high enough for people to click into it.

That must be it. It would have been nice for the original post to include this information.

I can confirm: https://i.snipboard.io/0wmnSv.jpg

We can also see that lately there are more questions than answers, which shows that most experts are no longer that active, or that there are more beginners and fewer experts overall.