I think I donated to Wikipedia for three reasons.
First, every time I have a question, Wikipedia is there to answer. I have gained much knowledge through it, and I am grateful for its existence.
Second, I like Wikipedia’s vision: to give a free encyclopedia to every single person on the planet, in their own language.
Third, I like that its founder Jimmy Wales is doing everything he can to keep the vision alive. Jimmy could easily have started running ads like other websites do. He would make a few extra million dollars. Wikipedia would still be awesome. But he didn’t, because that would not be aligned with his vision.
Wikipedia needs donations to stay alive, and so I will happily support it.
I think it is pretty awesome to live in a world where practically all knowledge is accessible to everyone. It is even more awesome that I can contribute a part – however trivial it may be – to make this possible.