Form elements created with AJAX aren't sending values through form_state
Move all form building activities from the callback to the form build function.

The form elements you add in the callback go directly through javascript to the DOM in your browser. You see them as normal form elements, but the form API doesn't know that they are in your browser and will ignore them.

Edit for the questions in comments:

In the form build function you know that you are rebuilding because $form_state is filled with data. On the first run it is empty.

You have the number of columns in the value of the select element.

You should wait with handling of the configuration data until submit.

In general an ajax form should have the same code in form build as a normal form, because if jquery is not available, ajax will fallback to a normal rebuild.