Going by the complains people on this site have about editing wikipedia, it's not funding that's driving people away, it's the Stack-Overflow-like situation where certain editors are extremely quick to delete content and resist the submission of new content.
Is it possible that this effect is due to a lot of "low-hanging fruit" articles being essentially complete? Back in '07 there were a lot more empty pages to fill on topics of broad interest.
This thread (or rather, this whole topic) is more about funding/business model than anything else, yet gp points to the slight decline in the number of active editors that is quite easily explained by other factors (see other replies) as evidence that Wikipedia is “not doing that well” (cerntainly not financially, so in what way exactly and how is that relevant?). Now that’s something hard to follow.
The thread is about whether a for-profit service for Wikipedia is a good idea. The healthy finances show this is completely unnecessary for keeping the lights on, while the "slight" decline in editors (a huge drop relative to where it should be with continued exponential growth) shows that the health of the community is much more concerning. That suggests that the decision should be informed much more by its impact of community healthy than its impact on finances. The more Wikipedia becomes an organization monetizing the work of volunteers, with that money spent on cancerous overhead while the contributor tools languish for decades without meaningful improvement, the fewer people will want to volunteer.
Maybe people have moved on to wikia (now called fandom) where you can focus on a specific series or topic. The number of users seem to heavily favor fandom too.
And it's a big loss to the Internet, because unlike Wikipedia, there's AFAIK no easy way to download all the content despite most of it being under the same license, and because unlike Wikipedia, site functionality is significantly impaired unless you enable their obnoxious Javascript.