That's one thing. But there's another. I've done years of fighting sports training with half the local (sort-of, they get called out pretty far, sometimes even flown somewhere) SWAT team. Including the commander. If you think even such a team will go charging into what might be an ambush, you're insane.
It does not work like in the movies. If you're in your house and someone is trying to kill you with a weapon, it will take the cops 15 minutes to your door ... and 30 minutes before they come in, minimum. If a unit has been lost (meaning a cop already got hurt), it will take hour before they come to the door, minimum. Some places (such as the court house) have different rules.
As soon as a unit has been lost, they will FIRST do a cost-benefit analysis of retaliating at all. And, especially in large cities, that analysis will regularly come up with something akin to "just let them deliver the drugs and do ... nothing" or "just let them go". Even when non-lethal (and "non-lethal" as in a knife) weapons are used they may refuse. You see, not getting maimed (even a little bit) is a thoroughly essential part of having any sort of career, and the treatment wounded cops get certainly does not justify self-sacrifice. The kinder logic is that criminals don't stop after one crime. If it's needed to stop them, there will be another chance.
Working this way means that for even a large metro area they can maybe handle 5 to 10 serious situations at any one time. Police weapons, even the big ones, do not defeat even relatively small determined militias. And the police will abandon neighbourhoods long before it comes anywhere near this point.
If they truly the think the situation will escalate without end, they may go in. That, by the way, generally means snipers, not knocking down the door. If they don't think the situation will escalate, or if there's too many people, or ... they will just let it be.