Has "praying the prayer" become a substitute for baptism?

Now when they heard this they were cut to the heart, and said to Peter and the rest of the apostles, "Brothers, what shall we do?"

And Peter said to them, "Repent and be baptised (immersed) every one of you in the name of Jesus Christ for the forgiveness of your sins, and you will receive the gift of the Holy Spirit.

Acts 2:37-38

I'm wondering if there's a reason why we don't follow NT practice of baptising new believers.

We make it an optional extra they can get around to once they are mature enough.

The NT practice was to include baptism in the conversion experience. We've taken it out and substituted "praying a prayer" of commitment. In the NT there are no examples of "praying a prayer" of commitment. Instead people are challenged to be baptised immediately.

Here's what I'm thinking: instead of taking people to Romans 10:8-9 when they are ready to make a response to the gospel, why don't we take them to Acts 2:38? That verse has the added benefit of including the gift of the Spirit in the experience of conversion.

While we're on baptism, Eckhard Schnabel asks why we use the Greek term when there is a perfectly good English word — to immerse, to be immersed, immersion. That's what the Greek word means. "Baptism by immersion" is a tautology, baptism means "immersion".