Running the structure is expensive. According to Wikimedia, base salaries are 20000 USD to 30000 USD per month or so. It has to be paid somehow.
https://meta.wikimedia.org/wiki/Wikimedia_Foundation_salarie...
https://meta.wikimedia.org/wiki/Wikimedia_Foundation_salarie...
I personally don't want my money spent like that, so I don't donate.
In 2005, they were doing 1.6 billion pageviews monthly, with a bandwidth budget of $5000/mo and a staff of 1.
By 2015, their pageviews had gone up 11x. Their bandwidth costs had gone up 33x, and their staffing costs 1250x.
In my view, both bandwidth and staffing costs should be nearly linear with pageviews - and ideally a little sublinear.