Regardless of whether the springs are perfectly square ground with parallel ends. The standard springs are MUCH more likely to buckle, and this buckling results in the middle of the spring deflecting and rubbing on the threads.

Just try and compress a rear AE green spring and then try and compress a kyosho gold rear spring. I will be willing to bet money you cannot compress the green spring all the way down with JUST your index finger and thumb without it shooting out, while the BB spring will compresses easily.