Those who have trained their thumb will understand what I am about to attempt to explain. I hope I write this well enough for all others to follow.
Even when unobstructed by limbs, other people in the boat, engine cowlings, or other objects, anglers rarely make a precise vertical back cast and forward cast in a direct line at the targeted area.The listed objects can make the off line variation worse. Now consider that head winds, cross winds, and even tail winds affect a cast. As a result the release point for the line varies by far more factors than distance, rod length and load, line weight, and lure weight.
To become accurate under the above circumstances, one must learn two things. First you become skilled with your back and forward cast. Second you learn to control all the factors and do so through adjustment of not only speed but also trajectory and direction AFTER THE CAST IS MADE. No one is that proficient with a spinning rod. However if you watch veteran baitcasters, you will see them use their thumb to feather the spool speed, as well as move the rod tip to change the bait direction, and then stop the bait at the correct distance. With a spinning rod in your hand, if you attempt any of these methods, the coils of line disconnect you from the bait. In fact, the coils accentuate the trouble in cross wind situations. There is a reason all the casting accuracy contests were won by bait casters - even back in the days of the knuckle duster.
As a further comment, someone mentioned that certain famous anglers used spinning gear almost exclusively. Billy Westmoreland was one example. He was (I assume he has passed) an outstanding fisherman and he did rely heavily on spinning gear. However he fished highland reservoirs with small hair jig and rind baits weighing 1/8 ounce and accuracy was not vital. And I read once that when he fished lowland tournaments, he switched to bait casting equipment.
I carry a spinning rod in the boat an days I will be throwing Shad Raps and crappie jigs. Everything else is on a bait cast rig.