Because in Inferno, Life Leech is cut to 20%. I wrote about it under 'sustain' in the initial post. For example to beat 2k LOH, assuming you get a massive 10% life leech :

DPS : 100k
Life Leech : 10%

Total life leeched from damage : 10k life

Inferno life leech rate (20%) : 10k * 20%

Total net life leech : 2k
As you can see, unless you're outputting massive amounts of damage consistently (Like over 100k DPS)...under current game mechanics LOH is more efficient.

Yeah but who runs with 2000 LOH.

Even top tank barb streamers run at 800.

I understand what you're saying bro.

Monks hit faster, so your LOH will scale off additional hits. Barbs stacking damage will hit harder, so more damage gets converted into life. Will probably need to spend a bit to test out which is viable.

i thought in inferno, life leech percentage is reduced or something?

LoH still better until your barb is dealing dmg in the 6 digits or doing massive aoe.

also, barb's own life leeching skills are based mostly on your maximum hp, and that isn't affected by inferno penalty AFAIK