From NBC:
“Police wear body armor. Why would a community member be driving around in body armor?” Craig asked.
In this particular case, it’s because the bad guy wanted to protect himself from being shot while committing a crime. No surprise there. (It’s worth noting that felons are prohibited from owning armor.)
Leaving aside the fact that the wearer in this case was a criminal, I certainly don’t think it’s unusual at all for an ordinary, non-felon private citizen in a crime-ridden city like Detroit to consider wearing body armor. Type IIA or II armor will protect against the majority of common handgun rounds which one might encounter in a place like Detroit.
Is it uncommon for private citizens to wear armor? Sure, but it seems odd to question why a private person might want to wear armor. The answer is simple, and it’s exactly the same reason why a cop wears armor: they don’t want to get shot.