Sorry you didn't get to see stones. As for reasons, could be all the ones you mention. Didn't I tell you to follow the steps *exactly*? I have heard that messing with the time even by a few minutes can derail it. It doesn't matter if you spend a miserable night. You can deal with it, as it helps in the long run, so next time suck it up and follow all the steps properly!!!
I never change my diet at all. I eat normally and just stop at 1:00 on the day of the flush. If I'm hungry after that I drink apple juice. Plan on sitting at home doing nothing and not being that comfortable, it's not a big deal for one night to be hungry, nauseous, or whatever. Soon it will be over. (This is my experience and I get a lot of stones out--have done 10 flushes now, only one where I didn't get any, maybe #3 or 4).