SWAT team?? I'm talking about patrol officers. Yes I have been trained, but being trained and being practiced are 2 different things. Also "active shooter" involves teaming up with the first 4 officers on scene, moving as a team (team leader(point) left cover, right cover, and rear guard) quickly to contact. No 3-5 second rushes, almost a jog, as a group, with one person walking backwards, toward where the gunfire is coming from.
Think about it, it's kinda tough to do.
The idea is as quickly as possible get to the BG so he stops shooting GG's. Going cover to cover slows you down. Plus inside most building there is very little cover just concrealment. THe team sticks together to try to keep the possibilty of "friendly fire" down. Tough to shot your teammembers if your shoulders are touching. Plus if its done right the front 3 on the team are all firing at the BG, at the same time.