Powergamers.
As a Tribunal I had only vigilance, which is nice to use to know are there thieves in game. Thats all. I've fought in the city with criminal only once. Do you think Seantryn is crowded city? hah.
It takes time to get promoted to Hamsah at least, where you can do some action. And what are the chances that you will meet criminal in your PK range when be in duty (assuming you are not a hero)? Not much if compare with chances of PK when you just hunt actively. I mean that other cabal's power are better since you do not have to sit and wait, you can use them on hunt.
Empire has not really good powers, but it has numbers. Allies are very important for ap. Grab someone from shadow/blade sect and go on eastern. Summon + trip/bash/strangle/bj = PK.
Scions simply have much better powers and much less restrictions. This is cabal for powergamers, not Trib.
I went for Trib because its just a bit easier for newb and for personal OOC reasons (always liked that on-duty system and to be "bad cop")