"What's the resistance to using UTM?"
One thing is a small factor, but I learned land nav way back when they were still trying to perfect the magnetic compass, so I grew up with lat/long. Also, I think in terms of feet or yards or miles, not meters and kilometers. From time to time, I have converted over to use UTM, but so few of the maps that I've seen have a very robust implementation of UTM. I've also converted over to use the Military Grid and used that for a time. Some of the topo maps use both lat/long and UTM, so it really doesn't matter.
Some of the problem comes from the datum. So few people deal with the datum when they refer to lat/long, UTM, Military, or anything else, and they don't seem to realize how far that can skew your apparent position. I contacted a GPS manufacturer one time about the database that one receiver product used, and I asked about the datum. Their answer was, "Huh?"