It’s intended to be a sign of humility that the cardinal is addressed by his Christian name first (“Francis”), then by his station within the Church (“Cardinal George”). Although a comma is not used in writing it out, one is really saying “Francis” (pause) “Cardinal George.” It is a pious custom however; writing it the other way (“Cardinal Francis George”) is also legitimate.
Such customary marks of humility by those in the ecclesial hierarchy are not uncommon within the Church. Another example is the custom of some priests, particularly within religious orders, to lowercase the title in their signature. Written out it might look like “fr. John Smith” and is an acknowledgment that the priest’s spiritual fatherhood is based on God’s own Fatherhood from which all spiritual fatherhood is derived (cf. Matt. 23:9).