Because I’m a jerk. That, and because Jesus said this,
When you give alms, do not blow a trumpet before you, as the hypocrites do in the synagogues and in the streets to win the praise of others. Amen, I say to you, they have received their reward.
But when you give alms, do not let your left hand know what your right is doing,so that your almsgiving may be secret. And your Father who sees in secret will repay you.