Why is the ROS bridge required

I am supposing the ROS1 bridge is required for gazebo and the associated robot controller, which, I am guessing are ROS1 based.

Is there a plan to move this course to entirely ROS2 to remove the bridge complexity ?

You are right. ROS1 is also required for creating the base MoveIt package since the Setup Assistant tool has not yet been ported to ROS2. We plan to move it entirely to ROS2 once Moveit2 development is a little bit more advanced.

Package ‘ros1_bridge’ not found