When being towed forward, the tow bar arms are in tension and when trying to backup,the arms are in compression. Any time you put a column such as the arm, it is not nearly as strong as in tension. The arm is more likely to buckle.
Additionally, the caster on the vehicle front wheels is set to keep the stability when moving forward. When the tow vehicle is reversed, the caster is opposite of what it needs to be for stability. In addition, the toe is set for forward motion, not to the rear. This is why the tires will tend to turn or flip when you try to back up.
Amateur Radio Operator (KE5DFR)|Full-Time! - 2012 6.7L Ford Crew Cab Dually -2013 HitchHiker Champagne 38RLRSB - Travel with one Standard Schnauzer and one small Timneh African Gray Parrot