Why didn’t the cops storm the building instead of holding back the crowd?
Because cops are now federalized bureaucrats. Their only masters are politics and their own bureaucracy.
Because they were cowards. Afraid of getting hurt or of getting in trouble / blamed for what happens after they go in. So they stood around and let it happen while they formulated excuses.
Citizens need to apply pressure to restore their Second Amendment Rights and duties. Police have no skin in the game.