I can't see any real advantage of BB7s in something like the TD, if anything the adjustments are faff you need to avoid when racing but there's genuine advantages for really remote touring or sub-zero stuff.
Most of the bikepackers using them just buy into the simpler, more fixable nature of any part options so they go on bikes with rigid forks, thumbshifters, SS etc.
What's the chances of sus forks, hydro brakes, rapidfires etc going wrong? Unlikely really. But sods law says it'll happen in the middle of an amazing ride and risk spoiling an amazing trip*. Stripping out potential issues and having a fix for any you can't eliminate is probably more about the Ray Mears mentality of bike touring than the actual risk, but if you remove 3 or 4 possible things that can go wrong the bike does become more reliable.
*My friend rides a SS with adjustable dropouts, he's had it years and rides it hard, a very trusted bike. Halfway through an 11-day trans-alp bikepacking trip his dropout wouldn't stay tight anymore, it had destroyed itself. It waited until the middle of the best ride we'd all done, ever, to do that.. )