Why do we only genuflect to the Eucharist and not fully prostrate ourselves before God?
As a matter of fact we do at certain solemn events. When a man is ordained to the diaconate and priesthood, he makes a full prostration before the altar. In most religious institutes when a person makes vows as a religious, he or she also makes such a prostration, usually when the gathered assembly is invoking the Holy Spirit.
It is not required more often because not everyone is physically capable of making such a prostration and also because for a Church full of people, there would not be enough room. What is most important is the desire to make an oblation of ourselves to God interiorly.
Fr. Vincent Serpa, O.P.