Couldn't it be said Wikipedia is basically complete? Which would explain the declining number of edits

A comprehensive encyclopedia is never complete.

Never is a very, very long time.

At some point in an encyclopedia's lifetime, it's "complete enough" that you'll see an excess of authors. "Compiling the world's information" and, past that, "compiling current events as they happen" (with a side of "occasionally improving/updating old articles") need very different numbers of authors.

> Couldn't it be said Wikipedia is basically complete?

No.

Serving pages to logged-in users is very costly to Wikimedia. Edits are even more costly.

What I'm trying to communicate is that Wikimedia has challenges, possibly exacerbated by Google's behaviour, but the challenges are not money. Wikimedia is not a for-profit corporation, it's a non-profit with a mission to collect and distribute knowledge. Google distributes pieces of that knowledge, but does not contribute to the collection of new knowledge.¹ Wikimedia has all the money it needs, and is getting more money from more people all the time. It does not have all the contributions it needs in the form of new knowledge, and by many measures the new knowledge it gets is decreasing.

tl;dr

The monetary cost does not really matter

1. It does contribute money, which Wikimedia does not need.

the decreasing number of edits likely has more to do with the obnoxious edit policies and power users who will stamp down on any new users trying to edit, rather than a few less pageviews directed from google search results.