I think I know why this practice gets such a hold on people. I mean aside from the obvious ocd lure...
Receiving physical adjustments from a teacher each day is a real tough thing to put the body through...
Small (or not so small) adjustments by experienced teachers profoundly affect the body, and at the end of the day there's a level of soreness and aching, which creeps in as the muscles repair themselves...
It's kind of the same soreness you'll get about 8 hours after a physical fight...
So I'm suggesting that there's a survival endorphine which is released, and it's making the ashtangi feel as if they've survived some dangerous, or life threatening event (like a street fight)... and they want more, because it's a safe high.
This idea just occured to me after 3 days of adjustments in forward bending, hamstrings have no idea what's going on.
It's great...