You may be forgetting that the bigger donations (as amount of Bitcoin) were made when Bitcoin was small, most probably under 200$.
Many of the spent Bitcoin may be also at low prices. This means that if you calculate everything at today's price of Bitcoin you'll be awfully wrong.
Mind boggling that it took 20 posts for this to be mentioned.
These days if you're happy to donate 50 BTC to become an official donator then more power to you but you're likely to be in a microscopic minority. Once upon a time that was 50 bucks. The origins of this forum came together before Bitcoin itself even had a price.