Tenor or Smaller to a Baratone with different cords

I have just got a baratone. It will take a time to get used to it having been using a tenor.

I was wondering why the cords are different. For example a G chord will become a D cord. I understand the strings are different, so it will need different finger shapes.

What I dont understand is why a different finger shape doesn't have the same cord name. So G remains G with a different finger pattern. I assume it is because they are not exactly the same sound.

I appreciate that the cords move 5 frets. But why is a G not a G with different finger placings.

I am sure it is obvious when you know why.

I was wondering if someone could explain the logic and the reason for this.

Thank you in advance for your help.