Rotation axis A for grbl

I have a machine that uses grbl, and now I want to use a rotating attachment. I found that there is a big difference between the Gcode generated by using the Z-axis and the A-axis. I want to ask how this difference comes about. According to my understanding, I just use a different motor.

My rotatry Setup:
image

Gcodes:

I want to know why the speed parameter F keeps changing when using the A axis, but not when using the Z axis ?