I'ma make some pointless wild guesses and hopefully I might make sense:
with increased poison procs and mutilate crits, you get higher burst under lifeblood than using hemo and waiting on 5 point eviscerates with the mediocre damage from hemo.
For sub in pugs, I would guess the high dodge % for survival, high crit and above average white damage for taking down stragglers.
That's just me wild guessing, though. As far as I know I could be completely off since I don't play a 19s rogue.