(a) I currently have more money than I need to cover my basic needs. (When I didn't have this, I didn't contribute to stuff.)
(b) I recognize that many of the free things I love couldn't exist or would be significantly worse without voluntary contributions.
(c) I want to live in a world where quality free things can get crowdfunding, so I lead by example.
(d) It makes me happy to help people who have freely shared their value with me.
FYI, your apparent lack of (d) is the reason you're getting downvotes. Nobody likes an ingrate. Lacking (a) is more socially acceptable, I think.