parametera entering approach with rosrun and roslaunch

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Hello, my question is regarding what I noticed during my work with kinect2_bridge.

While I was launching the node via roslaunch, I was adding parameters this way: 'roslaunch kinect2_bridge kinect2_bridge.launch publish_tf:=true'

However this doesn't work with rosrun, which rosrun I used: 'rosrun kinect2_bridge kinect2_bridge _publish_tf:=true'

If I delete underscore before 'publish_tf:=true' the parameter will not be added.

Thanks in advance!