Robot model is not loading if using namespace __ns:=sim1

[ron007d]

if I use __ns:=sim1 arg while launching the gazebo.launch the robot model is not showing + the gazebo is paused due to that.
launch file
https://github.com/ron007d/ros_pick_and_place_simulation/blob/main/src/simple_simulation/launch/simple_simulation.launch
urdf file
https://github.com/ron007d/ros_pick_and_place_simulation/blob/main/src/simple_simulation/urdf/simple_robot_with_camera.xacro

why the model is not showing if I use namespace for gazebo spawn model

cmd to run

roslaunch simple_simulation simple_simulation.launch __ns:=sim1