I can do better than a lot of them and have. But I don't protest to be good. That was not my point. My point is that some of them are self appointed 'great' and far from it.
I know some of those commentators that you call "simply bad", just sit there for 8-12 hours a day behind the mike doing very little good:

They stop the players from starting the match before the system is in place to record the match.
Set the cameras.
Choose the main cameras.
Check the audio to make sure they can hear themselves and the other commentators clearly and do an audio check with the listeners.
Learn which other cameras are operating from which angles.
Set the system for broadcast.
Set the system for recording.
Choose and start the appropriate sponsors' commercials.
Open the match.
Signal the players to begin the match.
Keep up with the match.
Periodically check the chat room to make sure that the viewers aren't experiencing any inconveniences that can be corrected, while doing a little moderating when necessary.
Update and compare the scores on the screens with the scores that the players are marking or not marking.
Dealing with questions from the pool players, pool fans and management that are regularly being asked of them despite the fact that they are there to primarily provide commentary for the match.
Bring interesting pieces of information to the viewers that isn't being fed to them by a crew, keeping the commentary as interesting as they can despite the long hours and multiple days of grinding through the same problems every day, keeping a positive attitude the whole while.
Closing out the match.
Reminding the fans about the sponsors and upcoming events.
And probably another dozen things that don't immediately come to mind.
I'm sure glad you are confident that you can do better than a lot of those commentators you call, "simply bad".
The funny thing is, I can't think of a single commentator who has said that he was "great".
JoeyA