Compound shooters usually use a right wing or right helical due to screw-in heads, but why does it seem that LW or left helical is more predominant among trad shooters?

Its very important if you are shooting off your knuckles so you won't get cut. If you shoot off an elevated rest or the shelf, it won't matter much.

I've never really noticed that LW is more prominant in trad archery. I've got clamps for both. I tend to use whichever I find a good sale on. I've never seen a hoots worth of difference in arrow flight off any of my bows.

Why would you get cut when shooting off of your knuckles?

Rt wing helical will put the leading end of the bottom hen feather right on top of the knuckle for a right handed shooter. Left wing will move that end off the knuckle. For left hand shooters, it's the opposite of course.

Now, most of us are smart enough to dab a drop of glue on the ends of our feathers to keep them secured. So most times you can't get cut. But.... If that leading end of the feather gets loose and pulls up, I guarantee ya, it'll cut you and it stings like a sonuvagun. Even worse is when it doesn't cut you but, instead, that end buries up into the flesh and breaks off.