There's actually been loads of both small and prominent organisations accepting bitcoin. Save the Children, American Red Cross, EFF, Greenpeace, Hal Finney's ALS fund, Mozilla, Wikipedia etc etc.

If you look at the Humble Bundle for example, Linux users consistently outdonate windows users in voluntary transactions every single time. Bitcoin is a bit like that, too, both because of the type of crowd and because people are eager to spend and use bitcoin and to support charitable organisations that participate in the bitcoin ecosystem.

Lastly, it's an interesting angle because payment processing costs 0% for charities, yet the payout is in dollars, euros or a bunch of other currencies including bitcoin (just like for any other business btw if you use Bitpay)

It very much seems like charity is one of bitcoin's biggest usecases at the moment. Not saying it's the best thing ever, but we shouldn't discount it as there being no interest and no charitable bitcoin users.