People who try to compare to arma/insurgency haven't played PR mod bf2.
The reason why this kickstarter got funded so quick is cause the mod is that good.
Your question is kinda like saying why play cRPG doesn't age of chivalry do the exact same thing?
But anyway arma is not built for pvp, altho there a pvp mods its never the same. Insurgency is build for pvp and actually has quite similar gunplay to PR but its also simular to counterstrike.
In insurgency theres no vechicles, the maps are tiny, indestructible, static, the rounds and short and meaningless. its a fun game but very casual despite the "hardcore" gun damage.
In PR rounds last hours, teams build up bases, it can actually be realistically boring - but that just makes it feel all the more realistic when you do spot an enemy and you don't know whether its a civilian or a jihady pointing an RPG at you precious APC which you literally need to not blow up to win the round you just been playing for last hour!
Adrenaline makes game feel more realistic than polygon count.