The technical, legal, and administrative costs of Wikipedia are not the problem. There's plenty of funding for that, and if the site were truly in jeopardy there would be a long line of institutional donors ready to support it.
The problem is that there's a bloated global administrative organization that doesn't actually help the core projects, and which drives up costs immensely. There are people in charge of partnerships who fly around the world looking for the next great thing, trying to get the foundation's foot in the door so that the empire will expand. There's money spent handling administration, legal matters, and software maintenance for projects like WikiNews, WikiBooks and WikiSpecies that, after using up more runway than Wikipedia did before it went aloft, still don't show meaningful signs of growth and relevance. There is money and effort being spent to maintain an egalitarian spirit and level playing field by supporting Wikipedia projects in dying languages, even though there is ample evidence to show that beyond the top 100 or so languages worldwide (maybe fewer) there aren't going to be enough contributors. There is money being spent on international staff travel that serves no useful purpose beyond demonstrating that the staff is globally engaged.
Perhaps these are all laudable projects and the effort is worthwhile. But the major institutional donors don't agree, and so the money isn't coming in.
If a foundation were created with a mission limited to supporting the largest 10, 20, 50, or 100 Wikipedias plus the commons image hosting platform, using a small administrative and technical staff in a single location with a token travel budget, there would be plenty of money. There would be enough money to build an endowment.
The smaller Wikipedias, the side projects, the partnerships, the in-country "chapters" could all be spun out to succeed or fail on their own merits. But that's not the way the foundation wants it. They want something bigger.
As though Wikipedia isn't enough of a success to be worth maintaining.