My response did not reflect my opinion but the opinion of the Park Service.  The OP asked "why" and that is the answer.  We can all complain and jump up and down but it doesn't do any good.  The same "problem" exists in many other similar areas.  Why can't mountain bikes be ridden on trails in the Park but you can ride a horse that causes 50x more trail damage and horses are generally unpredictable when encountering walkers?  Same reason.  It's "new" tech and its much easier to just say no