In most jurisdictions, there is a limit on how many shells you can load a shotgun with for hunting. Since most shotgun sales to civilians are primarily for hunting, the manufacturers include these "plugs" by default.
Good luck with your 500. I've had mine (500 combo) for over 20-years and it was my primary HD shotgun until I picked up an 870. The only reason I bought the 870 is because our Agency only issues the 870 for patrol work. And having an 870 of my own allowed me to get proficient with it.
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