Adults don't want their hair messed up or water spots on their clothes. Remember how Christians were baptized in the early church - naked, by immersion. And after you came up from the water, they wrapped you in a white robe and poured scented oil on your head and made the sign of the cross in it as it ran down your face. Clearly before carpeting. There was nothing neat and tidy about it.
Salvation is a birth, and there is nothing neat about birth.
I'm not a father, so I haven't had the joy of witnessing the birth of a child. I recall a Navy training film I had watch in college about delivering babies. I made it through the first two deliveries, but number three made the room wobble and the blood drain from my head. No doubt about it, birth is messy. And so is our new birth of water and the Holy Spirit.