Why is it not still in order?
Today there is just "one baptism" (Eph.4:4) and the "one baptism" is the one performed by the Holy Spirit (1 Cor.12:13).
Better question. What is the purpose of water baptism?
When water baptism was in order its purpose was to prepare the way for the Lord Jesus:
"In those days came John the Baptist, preaching in the wilderness of Judaea, And saying, Repent ye: for the kingdom of heaven is at hand. For this is he that was spoken of by the prophet Esaias, saying, The voice of one crying in the wilderness, Prepare ye the way of the Lord, make his paths straight" (Mt.3:1-3).
The people were to repent of their past way of living so that they could serve the Lord Jesus
"in holiness and righteousness " (Lk.1:75).
So when a person submitted to the rite of water baptism they were pledging to change their past way of living so that they could serve the Lord Jesus in holiness and righteousness in the earthly kingdom. But due to the unbelief of Israel the earthly kingdom has been postponed and it will not appear until the Lord Jesus returns to the earth, as witnessed by the words of the Lord Jesus here:
"And then shall they see the Son of man coming in a cloud with power and great glory. And when these things begin to come to pass, then look up, and lift up your heads; for your redemption draweth nigh. And he spake to them a parable; Behold the fig tree, and all the trees; When they now shoot forth, ye see and know of your own selves that summer is now nigh at hand. So likewise ye, when ye see these things come to pass, know ye that the kingdom of God is nigh at hand" (Lk.21:27-31).
When the kingdom was postponed then the rite of water baptism was phased out since that rite was to prepare a people to serve the Lord Jesus in the kingdom.