Despite the best effort of your piston rings and valve seals, some of your oil gets into the air flowing through your engine. In cars, and some bikes, this leads it straight through a catalytic converter. All those additives that are so great for protecting your engine are not so great for the catalyst. The thicker oils were not required to meet this phosphorus level. That is not to say that they won't.
Additives cost the oil companies money.
If they can get by with less, they might be inclined to do so. Standardizing the additive packages across all viscosity would also simplify their lives. Given this reduced level of phosphorous in some SJ oils, and the potential for it in others, BMW issued a service bulletin to address the issue. It said that SJ oils were not approved for use in BMW motorcycle engines. BMW did not consider it a supersedure and threatened to void warrantees if the SJ oils were used.