The tradition to kiss the hand of a priest, bishop, or the pope stems from the fact that the priest, bishop, and pope all celebrate the Sacred Mysteries and hold the precious Holy Eucharist in their hands. Their hands are consecrated for this purpose. Therefore, whenever we kiss the ring-bearing finger or right hand, we are acknowledging that they offer the Holy Eucharist to us.
Perhaps a novus ordo bishop or pope who discourages people from kissing his ring is announcing that he cannot offer the Holy Eucharist any more.