i'm pretty sure they merged early cuz they saw how crazy unbalanced the blue team would dominate the red team, that both the reward and the immunity challenge was non physical shit (everyone is basically on a level playing field with the reward challenge, just launch shit really, theres skill in that?).
from what i've seen, they usually merge at 12(contestants left) when it's a shitty season, and they are unsure of the contestants, this one, SJDR, FVF, one world, ozzy/coach, rob won, s21 were merged at 12, the rest were at 11, and HvV at 10.
pretty much would indicate that how the producers feel the season is going to go, is by when they want to merge, and for all intents and purposes, it's correct, they held back the HvV merge and got that awesome double idol, jt pass me note.
while one world, ozzy/coach, FvF, all those sucked.
and SJDS (even tho it was merge at 12) would have sucked if natalie didn't step up and dominate those retards. (but it seemed she could only really make her moves after merge anyway)