Shotguns are/were called “riot guns” in police use.
Your answer is “they” do not want cops to have the option to use them.
“They” know what is about to happen.
Cops need shotguns in civil disturbances. Many types of nonlethal rounds available. Control a mob without killing anyone.
This is political - force police to go from zero to deadly force in seconds, fomenting real violence. Despicable.
Chicago police should go on strike. Right now.