The key point of all organized religion is this: MONEY.
Churches have tithes, Chinese temples have 'oil money', mosques have 'zakat' donation boxes. All may have building funds.
Yes, giving is voluntary. But most believers are inclined to give out of their own conscience, to shy away from the guilt of not giving.
If you don't end up giving money, you'll end up giving your time. Either way, you'll give something.
As a result, the organized religions remain in business, and a rather profitable one too.