Choosing this of the many similar replies to answer to:
Full disclosure: I work for the Foundation in an engineering capacity.
The foundation has over 500 staff members. No organization is perfectly efficient, but by and large the money does go to good use.
Running a high-volume site like Wikipedia requires quite a lot of hard and soft infrastructure and supporting functions. The tech stack runs on its own bare metal (on the scale of a couple thousand servers) and its own CDN (to better protect against censorship and surveillance for the global audience, among many reasons), the total network currently has some physical presence in 7 different datacenter locations around the world, and there's all the redundant transport, transit, and peering network requirements that come with that. The live codebase gets new releases to production multiple times a week. There are many other side-services that run alongside the core MediaWiki codebase. There's constant network attacks on our infrastructure. There's all the infrastructure layer metrics and monitoring stuff. I could go on and on...
On top of all that (which implies reasonably robust techie staffing): there's a Legal department that has to defend against threats to the org from businesses and governments around the world and in general does a ton of amazing work in many different directions (my favorite example was our past lawsuit against the NSA in the wake of the Snowden leaks: https://en.wikipedia.org/wiki/Wikimedia_Foundation_v._NSA). There's all the usual corporate supporting functions, including finance, travel, talent and culture, etc. Can't fail to mention the Fundraising team itself, of course! :)
The foundation has a big job keeping the soft and hard infrastructure of the Wikimedia movement and Wikipedia going. The budget really isn't that unreasonable, and the endowment also isn't anywhere near big enough to replace our annual donation budget and ensure the org remains financially stable in the long run, yet. Usually when one of us goes to a conference and talks about our infrastructure, others are shocked to learn just how small our tech teams are for the jobs they're doing.