They have a confirmation that the owner is home, are told they are armed, but they just don't believe that the owner is actually armed or they don't care?
I think after decades of being able to commit whatever crime they want without repercussions has lulled them in to a false sense of security. How many unarmed people shout, "I have a gun!" and were proved wrong.
This just shows that all the criminals don't watch the news and must not know one another to talk about it, so it takes longer for the word to get around that when people say, "I have a gun!", some of them mean it.
If there are one or two shot every week, it makes me wonder how many get away with their crime while unarmed people are home. One 80 year old gentleman used a hammer. He understands that nearly anything can be used as a weapon.
As more and more of the good people of Detroit decide they aren't going to take it anymore, then things will change.
Eventually, the criminals will look for honest work, or move to another city that is less lethal for their illegal activities.