Because no matter how many people keep saying this is RP game, there will be trolls with the main purpose of destroying the fun for someone else.
It's what put me off from GTA-Online, just minding my own business and then just get blown up or shot, resulting in me just never leaving passive mode.
I love the idea of the game and would like to play as an EMT or firefighter, but it would destroy the RP if I had to arm myself to the teeth as those, just to protect myself from said trolls who just want to kill people.