Why Are Google Referrals To Wikipedia Dropping Precipitously?

Conspiracy? Arrogance? Indifference? The impetus may not matter as much as the perception. JL

Jim Edwards reports in Business Insider:

Google's own promo boxes on the top of search engine results pages are siphoning traffic from better-quality sites that normally would top results. The issue is at the heart of the EU's investigation into whether Google is abusing its monopoly in Europe to favor its own properties.
The amount of traffic that Google sends to Wikipedia has declined by more than 250 million visits per month, according to SimilarWeb, the traffic measurement company.
Roy Hinkis, SW's head of SEO, says the downgrade is a genuine mystery:

What I saw shocked me. Wikipedia lost an insane amount of traffic in the past 3 months. And by insane I mean that the free encyclopedia site lost more than 250 million desktop visits in just 3 months!

Here are the most recent numbers, in visits, per SimilarWeb:

• May: 2.7 billion
• July: 2.4 billion

SimilarWeb.com
Hinkis suspects that Google has changed its search algorithm to favour actual brands and company web sites over the Wikipedia entries that are about them:

Wikipedia has long since been a huge competitor for brands in terms of website traffic. SEO’s aren’t crazy about it, because it takes a huge chunk of our traffic.

To be fair, there is no evidence that Wikipedia's traffic loss is due to Google. We don't know how accurate SW's traffic sample is. And traffic goes through seasonal and news-cycle driven trends, and any of these could be affecting the site.
However, what Wikipedia taketh from other sites' traffic, Wikipedia also giveth: The site is so massive that it also drives a fair amount of traffic onward to other sites. But the less traffic Wikipedia gets, the less it can give.
Business Insider asked Google for comment but we have not heard back yet, so let's speculate.
One of the major trends happening at Google is the company's preference for inserting its own content above the content of other non-Google web sites, even when those sites may be better resources than Google itself. Google's goal here is to give people the best answer as quickly as possible.
Here is an example. If you're trying to remember who won the World Cup last year, you might get this Google result:
Google
If you click on that down-arrow that Google provides for the "roster and overview," you get a capsule on the German team. That might be all you need, and Google believes this is so useful it might save you a click.
The problem is that a few months ago that click might have gone to Wikipedia. And in fact the info in the Google box is drawn from Wikipedia. So on the one hand, this is good for Wikipedia (its info is featured prominently and the box does give Wikipedia a link). But on the other, Wikipedia thrives on clicks and this box is designed to save you from actually clicking through if you only need the bare bones info.
Several information aggregation companies are suffering from this, most notably Yelp. Yelp has repeatedly and loudly complained that Google's own promo boxes on the top of search engine results pages are siphoning traffic from better-quality sites that normally would have come top of the results.
The issue is at the heart of the EU's investigation into whether Google is abusing its monopoly in Europe to favour its own properties and distort the market for search traffic on competing sites.
We're not saying that's what is happening to Wikipedia. But it's certainly an unfortunate coincidence.