Why odom tf stays fixed in Rviz?

In the chapter “Creating a simulation of the robot”, when I run both gazebo and Rviz launch files and publish to cmd_vel topic, the simulated robot starts to move. In the Rviz, the Oom tf stays fixed.
Why Odom stays stationary?


The Odom frame should always stay fixed. Its the frame of reference for everything else in the simulation. Another thing is in real robots, that the odom frame respect to the real world, if there are errors in the odometry may diverge or jump when corrected with the ifferent odom correction systems