In addition to the factors Dale McGowan pointed to that support the giving culture of many churches ("As the Christian Church Crumbles, Is Humanism Ready to Step Up?" S/O 2018), I'd suggest one more: the promise that if you give charitably-especially if you give to the church--you're making a scripturally advised investment leading to a future heavenly payout in the afterlife. Though it's an ethereal incentive, it can be highly motivating.
Humanists of course don't have heavenly reward incentives or the structured giving that many...
