Its a matter of benefits vs. cost.
I wear a vest on duty and most of the time it is a PITA, especially now with all the humidity.
It does offer some protection of the vital organs, but most of the body is unprotected. And it will not stop a rifle bullet. So in a Colorado-type situation it would not have offered any benefit.
I draw the line at a 2" .38 that is light and small enough to not interfere with my life. If its not enough, well, so be it, I can't prepare for all possible dangers out there.