1. There are different kinds of 5.56mm ammo, they don’t all have the same construction or behave the same way. We don’t know what ICE are loading.
2. Even M855 green tip (which is what it sounds like you’re describing, or at least some similar variety of FMJ soft core round) can pierce lighter body armour and still be lethal. That means against an unarmoured target it’s going to have very little problem going in and out of a human body.
3. While I’ll grant that most softer varieties of 5.56 will be stopped by brick (again, we don’t know exactly what ICE are loading, but fairs fair, it was somewhat of an overstatement on my part), they will certainly have no difficulty going through drywall, wood, and other visual obstructions that could be concealing an innocent bystander. While it’s certainly true that something like a 9mm can also penetrate many of these obstructions, it will not retain nearly as much lethality when doing so, and it simply makes no sense to increase your risk of injuring a bystander every time you fire for basically no gain. If you fire an AR-15 inside a building (which, y’know, is where a bunch of people doing no-knock raids expect to be spending a lot of their time) you have a very high chance of killing an innocent bystander you couldn’t even see.

For more on this I consulted my wife who confirmed that she’s been shown videos in training of 5.56 going through multiple layers of dry-wall and still retaining lethal velocity. You can see this in this video here (https://www.youtube.com/watch?v=j3BlRPtCj2E) but know that this is also what professionals are taught about their weapons when considering targets, over-penetration and cover.