Because bitcoin enthusiasts are eager to donate money if it also helps their cause (creating a global decentralised currency not controlled by a central authority). Most of the people with lots of bitcoins (the people who got in at the beginning and can't cash out large sums because it would collapse the currency) are crypto-anarchists/anarcho-capitalists and oppose fiat currency. Acts like this is great PR and gets the word out. Stabilises the currency. It's a win-win. I know several people with 1000+ bitcoins. Sitting there not doing anything, they bought in at $0.10/e and are in it for the long haul. Not to make a quick buck. (And I'm here kicking myself for not investing when I was offered - thinking it would never go anywhere) And on top of that your bitcoins aren't going to get frozen (like the PayPal horror stories) there's little/no fee, many benefits, etc.