Universals are tightened against the axle hubs, so they dont slide around on that end but they slide around the diff cup end when the suspension arms go up and down.
Dogbones slide around the diff cup end as well as the axle end so if they are too short, they fall out, if they are too long, they hit against the cups and bind the suspension (preventing full travel). Unfortunately being short enough not to bind most off-road suspensions also means being short enough to fall out unless the dogbones stay right smack in the very middle between the two cups. This means you need some greased o-rings in both cups to act as springs to push the dogbones back to the middle. At just about any time, the dogbone is touching one of these o-rings so there's always going to be a little more friction with dogbones. Also, the dogbones are never really in the center of the diff cup since the cups are always going to be just slightly bigger than the bones and gravity would pull it down to the bottom of the cup when the car is stationary while the rotational forces would bounce it around inside the cups once it starts spinning. The same thing happens with the boney end of the universal shaft but at least the axle end is bolted to hub center (theoretically anyway).
I don't like the idea of dogbones on the front of any car since the steering combined with suspension travel puts quite an angle on the joint, and most axle dogbone cups don't really allow a sharp angle without binding.