Weights are cheap, easy to install, and the machine tells you how much to put on. Dynabeads you have to figure out how many to put in, break the bead, and put them in. I've successfully used Dynabeads in many Unimog tires and they definitely make a difference, but it takes a lot, considering they are ~$5/oz, that adds up compared to lead weights. Lead weights are old, tried tested and true. With beads, you might have to go back to the tire shop a few times until you get the right amount figured out, that's not economical for a tire shop.
The nice thing is they don't get ripped off when offroad, they dynamically balance when you get mud/snow/ice in the rim (to a point, they are no magic bullet but they work up to a certain weight). They don't blow out the valve stem when lowering tire pressure (if they are the right size) and don't attract moisture and clump and rust rims like powder.
They do take some speed to spread out and balance, and when you hit a good bump they scatter, but collect themselves shortly after.
And beads don't coming flying through the back of the cab in event of a blowout, like golf balls
(don't use golf balls...ever)