Not sure on the impetus or process behind this rule change, but the law in Alaska for motorcycles is that the dog has to be behind the driver to keep the drivers hands free and attention on the road. It makes me think of back in the day the ban on using anything for makeshift sails. Why?
One thing you have to look at is that cycling dogs into and out of the team and carrying them in a crate, humanely. Is really an advantage that caters more to the smaller sized musher like Dallas or his dad. Much has been made of Dallas background in wrestling, but in wrestling a wrestler only faces competitors in the same weight class. Dallas routinely races against a field of mushers much larger than him. An interesting study would be weigh in of mushers & sleds at the start & finish. Years ago, when Dallas & I & our generation were mere toddlers, there was conversation about a handicapping like in race horses for the mushers etc & sleds etc. so that the race would more accurately test dogs vs size.